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READING THE WEATHER

SHOWER BEHIND VALLEY FORGE

Courtesy of Richard F. Warren

READING THE
WEATHER

BY
T. MORRIS LONGSTRETH

ILLUSTRATED WITH PHOTOGRAPHS
By RICHARD F. WARREN

Number 43

NEW YORK
OUTING PUBLISHING COMPANY
MCMXV

Copyright, 1915, by
OUTING PUBLISHING COMPANY

All rights reserved.

DEDICATED
with love, to my grandmother
MARY GIBSON HALDEMAN
herself responsible for so
much sunshine.

CONTENTS

ILLUSTRATIONS

FORECAST

Science is certainly coming into her own nowadays,—and into everybody else’s. Every activity of man and most of Nature’s have felt her quickening hand. Her eye is upon the rest. Drinking is going out because the drinker is inefficient. The fly is going out because he carries germs. And for everything that goes out something else comes in that makes people healthier and more comfortable, and, perhaps, wiser.

One strange thing about this flood-tide of science is that it overwhelms the old, buttressed superstitions the easiest of all, once it really sets about it. For instance, nothing could have been better fortified for centuries than the fact that night air is injurious and should be shut out of house. Then, science turned its eye upon night air, found it a little cooler, a trifle moister, and somewhat cleaner than day air with the result that we all invite it indoors, now, and even go out to meet it.

Once interested in the air, science soon began to take up that commonplace but baffling phase of it called the weather. Now, of all matters under the sun the weather was the deepest intrenched in superstition and hearsay. From the era of Noah it had been made the subject of more remarks unrelieved by common sense than any other. It was at once the commonest topic for conversation and the rarest for thought. Considering the opportunities for study of the weather this conclusion, we must admit, is more surprising than complimentary to the human race. But it is so. The fact that science had to face was this: that the weather had been and remained a tremendous, dimly-recognized factor in our level of living. So talk about it all must. And science set about finding some easy fundamental truths to talk instead of the hereditary gossip about old-fashioned winters or the usual meaningless conversational coin.

Two groups of men had always known a good deal about the weather from experience: the sailor had to know it to save his life, and the farmer had to cultivate a weather eye along with his early peas. But the ordinary business man (and wife), the town-dweller, and even the suburbanite knew so few of the proven facts that the weather from day to day, from hour to hour, was a continual puzzle to them. The rain not only fell upon the just and unjust but it fell unquestioned, or misunderstood.

At last Science established some sort of a Weather Bureau in 1870, in our country, and after this had triumphed over great handicaps, the Government set it upon its present footing in 1891. An intelligent interest in the weather was in likelihood of being aroused by maps, pamphlets, frost and flood warnings that saved dollars and lives. Then suddenly, or almost suddenly, a new force was felt in every community. It was the call of outdoors. The new land of woods and lakes was explored. Men learned that living by bread alone (without air) made a very stuffy existence. Hence the man in town opened all his windows at night, the suburban majority planned to build sleeping porches, the youngsters begged to go to camp, their fathers went hunting and fishing in increasing numbers, and, most important of all, the fathers’ wives began to accompany them into the woods.

Thus, living has been turned inside out,—the very state of things that old scientist Plato recommended some thirty thousand moons ago. And among the manifestations of nature the weather is holding its place, important and even fascinating. For the person who most depends on umbrellas and the subway in the city needs to watch the sky most carefully in the woods. That old academic question as to whether it be wise or foolish to come in out of the wet was never settled by the wilderness veteran. The veteran’s wife settles it very quickly. She considers the cloud. When the commuter goes camping he rightly likes his comforts. A wet skin is not one of these. Therefore he studies the feel of the wind.

And so it comes about that the person who talks about storm centers and areas of high pressure and cumulus clouds is no longer regarded as slightly unhinged. Men are eager to learn the laws of the snowstorm and the cold wave; for, with the knowledge that snow is not poison and cold not necessarily discomfort, January has been opened up for enjoyments that July could never give.

Bookwriting and camping are both explained by the same fact,—a certain fondness for the thing. I wanted to see the commoner weather pinned down to facts. The following chapters resulted. They constitute a sort of Overhead Baedeker, it being their pleasure to show up the sureties of the sun and rain and to star the weather signs that can be relied upon. For, after all, even the elements, although unruled, are law-abiding.

READING THE WEATHER

CHAPTER I

OUR WELL-ORDERED ATMOSPHERE

If there is anything that has been overlooked more than another it is our atmosphere. But it absolutely cannot be avoided—in books on the weather. It deserves a chapter, anyway, because if it were not for the atmosphere this earth of ours would be a wizened and sterile lump. It would float uselessly about in the general cosmos like the moon.

To be sure the earth does not loom very large in the eye of the sun. It receives a positively trifling fraction of the total output of sunheat. So negligible is this amount that it would not be worth our mentioning if we did not owe our existence to it. It is thanks to the atmosphere, however, that the earth attains this (borrowed) importance. It is thanks to this thin layer of gases that we are protected from that fraction of sunheat which, however trifling when compared with the whole, would otherwise be sufficient to fry us all in a second. Without this gas wrapping we would all freeze (if still unfried) immediately after sunset. The atmosphere keeps us in a sort of thermos globe, unmindful of the burning power of the great star, and of the uncalculated cold of outer space.

Yet, limitless as it seems to us and inexhaustible, our invaluable atmosphere is a small thing after all. Half of its total bulk is compressed into the first three and a half miles upward. Only one sixty-fourth of it lies above the twenty-one mile limit. Compared with the thickness of the earth this makes a very thin envelope.

Light as air, we say, forgetting that this stuff that looks so thin and inconsequential weighs fifteen pounds to the square inch. We walk around carrying our fourteen tons gaily enough. The only reason that we don’t grumble is because the gases press evenly in all directions permeating our tissues and thereby supporting this crushing burden. A layer of water thirty-four feet thick weighs just about as much as this air-pack under which we feel so buoyant. But if these gases get in motion we feel their pressure. We say the wind is strong to-day.

As it blows along the surface of the earth this wind is mostly nitrogen, oxygen, moisture, and dust. The nitrogen occupies nearly eight-tenths of a given bulk of air, the oxygen two-tenths, and the moisture anything up to one-twentieth. Five other gases are present in small quantities. The dust and the water vapor occupy space independently of the rest. As one goes up mountains the water vapor increases for a couple of thousand feet and then decreases to the seven mile limit after which it has almost completely vanished. The lightest gases have been detected as high up as two hundred miles and scientists think that hydrogen, the lightest of all, may escape altogether from the restraint of gravity. One strange fact about all of these gases is that they do not form a separate chemical combination, although they are thoroughly mixed.

At first glance the extreme readiness of the atmosphere to carry dust and bacteria does not seem a point in its favor. In reality it is. Most bacteria are really allies of the human race. They benefit us by producing fermentations and disintegrations of soils that prepare them for plant food. It is a pity that the few disease breeding types of bacteria should have given the family a bad name. Without bacteria the sheltering atmosphere would have nothing but desert rock to protect.

Further, rain is accounted for only by the dust. Of course this sounds very near the world’s record in absurdities. But it is a half truth at least, for moisture cannot condense on nothing. Every drop of rain, every globule of mist must have a nucleus. Consequently each wind that blows, each volcano that erupts is laying up dust for a rainy day. Apparently the atmosphere is empty. Actually it is full enough of dust-nuclei to outfit a fullgrown fog if the dewpoint should be favorable. If there were no dust in the air all shadows would be intensest black, the sunlight blinding.

But the dust particles fulfill their greatest mission as heat collectors,—they and the particles of water vapor which have embraced them. It is in reality owing to these water globules and not to the atmosphere that supports them that we are enabled to live in such comfortable temperatures. For the air strata above seven miles where the tides of oxygen and nitrogen have rid themselves of water and dust absorb very little of the solar radiation. The heat is grabbed by the lowest layer of air as it goes by. The air snatches it both going and coming. The little particles get about half of it on the way down and when it is radiated back very little escapes them.

So it comes about that the heavy moist air near the earth is the warmest of all. It would, of course, get very warm if, as it collected its heat, it didn’t have a tendency to rise. As it rises, moreover, it must fight gravity, that arch enemy of all rising things. And as it fights it loses energy, which is heat. So high altitudes and low temperatures are found together for these two reasons. But after the limit of moisture content has been reached the temperature gets no lower according to reliable investigations. Instead a monotony of 459° below zero eternally prevails—459° is called the absolute zero of space.

The vertical heating arrangements of the atmosphere appear somewhat irregular. But horizontally it is in a much worse way. The surface of the globe is three quarters water and one quarter land and irregularly arranged at that. The shiny water surfaces reflect a good deal of the heat which they receive, they use up the heat in evaporation and what they do absorb penetrates far. The land surfaces, on the contrary, absorb most of the heat received, but it does not penetrate to any depth. As a consequence of these differences land warms up about four times as quickly as water and cools off about four times as fast. Therefore the temperature of air over continents is liable to much more rapid and extreme changes than the air over the oceans.

The disparity of temperature is also rendered much greater because of differing areas of cloud and clear skies, because of interfering mountain masses, because of the change from day to night, or the constant progress of the seasons. At first blush it seems remarkable that the atmosphere should not be hopelessly unsettled in its habits, that there should belong to it any hint of system. As a matter of fact, in the main its courses are as well-ordered as the sun’s. Cause and not caprice are at the bottom of the wind’s listings. Its one desire is rest.

CIRRUS DEEPENING TO CIRRO-STRATUS

Courtesy of Richard F. Warren

Cirrus clouds first appear as feathery lines converging toward one or two points on the horizon, often merging into bands of darker clouds, arranged horizontally. A sky like this appears when there is little wind. If the wind shifts to an easterly direction by way of north there will likely be snow within 24 hours; if it works around by way of the southwest and south 36 hours will probably pass before rain. If the mares’ tails, as here, are absent and yet the stratified clouds are present there is little likelihood of a storm. Cirrus clouds precede every disturbance of magnitude. Sometimes they are hidden by a lower cloud layer.

But rest it rarely succeeds in finding. Forever warming, rising, cooling, falling, it rushes about to regain its equilibrium. With so many opposing forces at work the calm day is the real marvel, our weeks of Indian Summer the ranking miracle of our climate. The very evolution of the myriad patches of air quilted over the earth with their different opportunities to become heated, to cool their heels, precludes stability in our so called Temperate Zone. But over great stretches of the earth’s surface conditions are continuous enough to discipline the atmosphere into strict routine. Conjure the globe before your eyes and you will find the scheme of atmospheric circulation something like this:

A broad band of heated air perpetually rises from the sweltering equatorial belt of lands and seas. The supply never ceases, the warming process goes on night and day, and to a great height the light warm incense mounts. Then, cooling, from this altitude it begins to run down hill toward the poles. This is happening all the way around the globe. So naturally the common centers, the poles, cannot accommodate all this downrush of air. Therefore as it approaches the goal it falls into a majestic file about the center, very much as water does in running out of a hole in the center of a circular basin. The nearer north, the cooler this vast maelstrom grows and the nearer has it sunk to the earth. It descends circuitously and, by the force arising from the earth’s rotation, is sheered to the right in the northern hemisphere, to the left in the southern.

Watching the water circle out of the basin you will notice the outside whirl is in no hurry to get to the center. This corresponds to the easterly trades of commerce, geography, and fiction. The direction of the upper currents flowing back to the poles is from southwest to northeast; but in our middle zones this becomes almost from west to east, is constant and is known to the profession as the prevailing westerlies.

Look up some day when wisps of clouds are floating very high. You will notice that their port is in the east, mattering not what wind may be blowing where you are. They are above the petty disturbances of the shallow surface winds. They follow a Gulf Stream of immeasurable grandeur. Onward, always onward, they sail, emblems of a great serenity.

Beneath this vast drift of air, which increases in velocity as it nears the pole, is an undertow from two to three miles thick. It is the movements of this undertow that affect our lives. These movements are influenced by all the changes of temperature and by the configurations of land. They take the form of whirls. These whirls may be small eddies, local in effect, or vast cyclones with diameters of fifteen hundred miles. Small or large they roll along under the Westerlies, translated by friction, and invariably moving for most of their course in an easterly direction, like their tractor above. They circle across the United States every few days. Their courses do not vary a great deal, and yet enough to make each one a matter for conjecture. And all the conjecturing centers upon the condition of the atmosphere,—the changing atmosphere which is yet so dependable.

The weather we are used to, the daily weather that catches us unprepared, and yet that does not mistreat us all the time is the product of these little whirls, which are so remotely connected with the grander atmospheric movements of our planet. Remembering this, we can at last come back to earth and set about our real business which is to see why certain kinds of weather come at such uncertain times and how to tell when they will arrive.

CHAPTER II

THE CLEAR DAY

We owe our fair weather to that department of atmospheric activity called anticyclone by the weatherman. The anticyclone is an accumulation of air which has become colder than the air surrounding it. This accumulation oftener than not has an area near the center where the air is coldest. About this coldest area the air currents revolve in the direction of a clock’s hands. And since this cold air is contracted and denser than its warmer environment it has a perpetual tendency to whirl outward from the center into this warmer environment.

One comes to think, therefore, of the anticyclone as a huge pyramid of cold air moving slowly across the country from west to east and all the while melting down on all sides, like a plate of ice-cream, into the surrounding territory. It is such an immense accumulation that often while its head is reared over Montana the first shivers of its approach are beginning to be felt in Texas and Pennsylvania. It does not extend equally far, however, to the north and west of its head, which is really sometimes where its tail ought to be. That is, a long slope of increasing pressure and cold will sweep in a gentle gradient from Pennsylvania to Montana and will then decrease by a very steep gradient to the Pacific Coast.

The anticyclone draws its power from the inexhaustible supplies of cold air from the upper levels. This air is very dry and accounts for the almost invariably clear skies of the anticyclone.

In winter when the intensity of all the atmospheric activities is greatly increased, the anticyclone develops into the cold wave. The rapidly rising pressure rears its head and rushes along upon the heels of a storm like a vast tidal wave at sixty miles an hour, tumbling the mercury thirty, forty, fifty degrees.

These cold waves first appear in the northwest. They cannot well originate over either ocean and a high-pressure area building up over the southern half of the country will not attain the sufficient degree of frigidity to earn the title, for even cold waves have been standardized by the Government. But although nearly all the cold waves choose Montana or the Dakotas as a base, they have at least two definite lines of action. Those which are born amid the mountains or on the great plains of Montana have a curious habit of bombarding the Texas coast before starting on their eastward march. It is not unusual for us to read of zero weather in the Panhandle and freezing on the Gulf while the mercury may still be standing as high as fifty in New York City.

It is this rapid onslaught from Montana to Texas that produces those notorious blizzards of that section called northers, during which the cattle used to be frozen on the hoof. The record time for a drive of this extent is about twelve hours and the normal about twenty-four which gives scant time for the Weather Bureau to warn the vast interests of the impending assault. When the cold wave, after following this path, does swing toward the Atlantic Coast, as most of them do, it has lost interest and usually produces only seasonably cold weather along the Appalachians.

Those cold waves that recruit their strength in Canada and enter the United States through Minnesota or, rarely, this side of the Lakes move along the border and supply intensely cold weather for a night or two to New England and the Middle Atlantic States.

Cold waves almost always follow a storm. The storm, being an area of low pressure makes a fit receptacle for the surplus of the high pressure, and since the whole business of the weather is to seek peace and pursue it, the greater the discrepancies the more violent the pursuit. Consequently we have the spectacle of a ridge of cold dry air following and trying to level up a fleeing hollow of warm moist air—but rarely succeeding. This principle of action and reaction is almost the sole principle of the weather and is nowhere more clearly demonstrated than in the winter’s succession of storm and cold wave.

In summer the anticyclones are not only actually but relatively more moderate than in winter. But their influence is still the same,—clear skies, cooler nights, dry, westerly winds. During the year the anticyclone furnishes us with about sixty per cent. of our weather. The cyclone is responsible for the remaining forty per cent. The weather depends on the cyclone for its variety and upon the anticyclone for its reputation. So it is well to be able to recognize an anticyclone when one appears.

The first and most reliable symptom of the approach of an anticyclone is the west wind. This sign is valid the country over, and is one of the very few signs that hold true for most of the North Temperate Zone. In summer over our country the west wind comes from the southwest, to be Irish, and in winter from the northwest. But for nearly all of our forty-eight states for nearly all of the year the westerly winds are those that bring us fair days and nights. And it is these crisp, clear days and cloudless, brilliant nights which we have in mind when we boast to English friends of our American weather.

The west wind is so popular because it has a slight downward flowing tendency. It also blows from land to sea over all America except the narrow Pacific coast. These downward, outward directions allow it to gather only enough moisture to keep it from becoming seriously dry. Its upper sources supply it with ozone. Its density gives it weight and by its superior weight it prevails. It dries roads faster than a brace of suns could do it. It is tonic. And curiously enough, although the anticyclone loads half a ton excess weight upon us we like it. The greater the burden the more we feel like leaping and shouting. Our good cheer seems to be ground out of us, like street pianos.

The reverse holds, too. For when the anticyclone moves off us and the cyclone hovers over us, removing half a ton of pressure, instead of feeling relieved we feel depressed, out of spirit. The animals share this reaction with us. In fact barnyards antedated barometers as forecasters, because all the domestic creatures, with pigs in particular, evidenced the disagreeable leniency of the low pressure areas upon their persons.

“Grumphie smells the weather
An’ Grumphie smells the wun’
He kens when clouds will gather
An’ smoor the blinkin’ sun.”

The only trouble about this rather extravagant tribute to the pig, versatile though he is, is that he can tell only a very few hours ahead about the coming changes and it takes so much more skill to judge what his actions mean than to read the face of the sky that the science of meteorology finally comes to supplant barnyardology.

The coming of the anticyclone is foretold by the shifting of the wind from any quarter to the west. The course that the center of the anticyclone is keeping may be watched by the same agency. Since the circulation from the cone of cold air follows the hour hands of a clock it follows that if the center is moving north of you the wind, blowing outward from the center, will work from west to northwest and from northwest to north and slightly east of north.

If the wind has shifted into the west on a Wednesday, it will likely be cold by Wednesday night and colder on Thursday. By Friday morning the wind will be coming from the north, likely, with the lowest temperature of all. By Saturday the cold will moderate, the wind will tire and gradually die to a calm or become weakly variable. The four day supremacy of the anticyclone will be over. But, mind you, there are a dozen variations of this routine. I am only suggesting a usual one.

If after blowing two or three days from the west the wind shifts to the southwest and south, you may know that the central cold area is passing south of you and that its intensity will not be great. While these anticyclones that float down and to the right of their normal path linger longer, they are never so severely cold, nor, alas, so uniformly clear as the others. It is a profound law of anticyclones and even more particularly of cyclones, that if they deviate to the right they weaken, if they are pushed by an obstacle to the left they increase greatly in intensity.

Occasionally the central portion of an anticyclone passes over your locality. Then the wind will fall. The frost will be keen and the cold will be notably dry and invigorating. In summer although the sunlight may be powerfully bright and the heat great, yet the air will have a buoyant effect, the body a resilience. And the nights will cool swiftly. Soon after the center passes from the locality a wind will spring up from the east with rapidly rising temperature and increased humidity.

The coldest part of the anticyclone is not, as one would suppose, at the center, but in advance of it; and its authority, like a schoolmaster’s, is rapidly dissipated after its back is turned upon a place.

The intensity of an anticyclone is measured by its wind velocity and by the degree of cold obtaining under its influence. But the greatest cold occurs rarely in conjunction with the greatest velocity of the wind. The calms that occur at sunrise enable radiation to take an extra spurt which pushes the mercury lower by a degree or so than happens when the wind is blowing. But, windy or calm, the period about sunrise is normally the coldest of the day, even extending in midwinter for as much as half an hour after sunrise, so slow are the feeble rays at restoring the balance of loss and gain of heat.

The greatest falls occur at the advent of the cold wave, no matter whether it arrives at ten in the morning or at midnight. If the temperature starts to decline gradually during the day, a further and decided fall may be expected at nightfall if the sky is clear. And if the temperature rises gradually during the night the normal processes are being displaced and a change from fair to foul is a surety. In summer the hottest time of day is not at noon, any more than the coldest part of the winter day was at midnight, for the reason that the sun can pour in its heat faster than the earth can radiate it, and the hour for the maximum temperature is pushed as far along toward evening as four or five or even six o’clock.

The average anticyclone continues its influence for clearness for about four days. Some, however, hurry the whole thing through in two. Others are interrupted by a more vigorous cyclone and are put to rout. Others are held up by an inherent weakness and are forced to mark time over one locality until strengthened or dissipated. And a few great ones hold sway over the country for a week. These choose the north-center of the country in which to locate. There they pile up the cold air until its very weight causes it to move majestically on. Its skirts sweep the Gulf coast where they are a bit bedraggled by invading cyclones. It gives the New Englanders a fortnight of nipping, brisk days and the mercury in Minnesota and the Dakotas does not emerge above zero. Once, in Montana, one of these refrigerating systems established the record of sixty-three degrees below zero. But in Siberia where the immense extent of the land surface collaborates with a prolonged night, an anticyclone built up an area of superior chilliness that left a world’s record of ninety-one below.

In summer a succession of these highs causes the frequent droughts of weeks which harass the West and New England. The air becomes so dry that it parches and then shrivels the green leaves. Any little cyclones that, under ordinary conditions, would suck in moist air from the Gulf and relieve the situation with a rain are dried out and frustrated by the unclouded sun. It requires a cyclone of great depth to overthrow the supremacy of these summer anticyclones.

While the anticyclone furnishes fair weather the sky is not necessarily or even usually free from clouds under its influence. In summer the evaporation during the long days overloads the air for the time being. Normally about eleven in the morning little balls and patches of white clouds dot the blue. These increase in number and size until about three in the afternoon when they will have grown little black bellies and fluffy white tops. By five they will have dwindled and by eight entirely vanished. These heaped clouds, known as cumulus, are a guarantee of a normal atmosphere and continued fair weather. They mean that currents of warm, moist air have risen until they have struck a level so cool as to cause them to condense part of their moisture. This condensation sinks until it enters a warmer stratum and the cloud is dissipated. The total movement is a reasonable exchange that preserves the equilibrium of the air, very much as a person bends one way and then another to maintain his balance.

In winter there is not such an opportunity offered and the few clouds that form because of the daily variation in temperature are flatter and are called stratus clouds. Sometimes these stratus clouds may cover the sky at midday, but in thin platings and not leadenly. In winter as in summer they tend to disappear toward evening. They are often accompanied by an unpleasant wind, but rarely by the snow flurry which is the “April shower” of the winter months.

But when the snow flurry does come there is no better sign for the woodsman of coming cold; it never fails. The morning will have begun brilliantly, but soon great summery puffs of cloud form and increase and darken on their under sides. Their tops are vague and wear a veil. It is the snow. The reason is simple. The coming anticyclone strikes the upper air before it hits the earth’s surface. The sudden cold causes rapid condensation. Hence the flurries. But the anticyclone is an agent of dryness, hence their short duration. Sometimes the veil of snow does not reach the earth. Sometimes it blots out everything in a spirited squall. But it never lasts long, except in the northwest states. And it is invariably followed by a period of colder weather.

In summer local evaporation may be so long-continued or so vigorous that the cumulus clouds cannot hold all their moisture content when cooled. A shower is the result, usually a trifling one and mostly without thunder. The great thunderstorms are always in connection with the passing of a cyclone. The small heat thunderstorms are only the indulgences of a spell of fair weather. These tiny showers are daily and sometimes hourly accompaniments of clear weather in the mountains. The air warms rapidly in the valleys and is speedily cooled on rushing up a mountain side and a threat and a sprinkle are the result. When a performance of this sort is going on nobody need fear unpleasant weather of long duration.

Another pledge of a clear day that does not appear too credible on the face of it is the morning fog in summer. In winter it is a different matter. In August and September particularly the rapidly lengthening nights allow so much heat to evaporate that the surplus moisture in the air is condensed to the depth of several hundred feet. By ten o’clock the sun has eaten into this lowest stratum, heated it and yet begins to decline in power before the balance swings the other way, so that a cloudless day often follows a fog in those months. About three mornings of fog, however, are enough to discourage the sun and a rain follows. Of course this is because the anticyclone with its special properties has been losing power.

When these conditions of clear nights with no wind follow the first two or three windy days of the anticyclone, particularly in autumn and spring, frost results. In winter the chances that a fog will be dissipated are rather slim. But if it shows a tendency to rise all may yet be well.

CIRRO-STRATUS WITH CIRRO-CUMULUS BENEATH

Courtesy of Richard F. Warren

The fine-spun lines of the cirrus proper drag this veil of whitish cloud over the sky. The sun sometimes is surrounded by a colored halo due to the refraction of the light by the ice crystals. But more often it vanishes behind the veil. The mottled clouds below the veil show that a rather rapid condensation of the moisture in the air is taking place. This sky is distinctly threatening, although the direction and force of the wind will more accurately foretell the severity of the coming storm. With this sky expect rain or snow within 12 hours.

An excellent sign of clear weather is this fact of the morning mist rising from ravines in the mountains. And even if you haven’t any mountain ravines at command the altitude of clouds can be observed. It is safer to have them lessen in number rather than increase, scatter rather than combine. The higher the clouds the finer the weather. And if the sky through the rifts is a clear untarnished blue the prospects of settled weather are much better than with fewer clouds and a milky blue sky beyond.

After the direction of the wind and the shapes of the clouds the colors of the sky are a great help in the reading of the morrow’s promise. And the best time to read this promise is in the morning or evening when the half lights emphasize the coloring.

Soon after the close observation of cloud colors has commenced the amazing discovery is made that the same color at sunrise means exactly the reverse of its meaning at sunset.

“Sky red in the morning
A sailor’s sure warning,
Sky red at night
A sailor’s delight.”

Christ seized upon this phenomenon to throw confusion into the Pharisees and Sadducees when they asked that He would show them a sign from Heaven. As Matthew reports it:—“He answered and said unto them, When it is evening ye say, It will be fair weather for the sky is red. And in the morning It will be foul weather to-day for the sky is red and lowering. O ye hypocrites, ye can discern the face of the sky; but ye cannot discern the signs of the times.”

The reasons for this contradictory evidence of color are not nearly so obvious as the fact itself. Taking the scientist’s word for it need not stretch one’s credulity overmuch if he can be followed step by step. He says that sunlight is white light, and white is the sublime combination of every color. If no atmosphere existed about us the light would all come through, leaving the sky black. The atmosphere, however, which is full of dust and water particles, breaks up these rays, these white sheaves of light, into their various colors. The longest vibrations, which are the red, and the shortest, which are the violet, get by and the rest are turned back, mixing up into the color which we call our blue sky.

If the dust and water particles grow so large and numerous as to divert more of the short rays than usual we get a redder glow than usual. This is most noticeable when the sun and clouds are near the horizon for the air through which they appear is nearer the earth and consequently dirtier. If these water globules mass together so as to reflect all the rays alike the result is a whitish appearance. That is why a fog bank, composed of tiny droplets, each reflecting with all its might, can make the sky a dull and uniform gray.

As evening approaches the temperature of the normal day lowers. As the temperature lowers it is the tendency of the moisture in the air to condense about the little dust particles in the air. And as these particles increase in size their tendency is to reflect more and more of the waning rays of light. Therefore if the sky is gray in the evening it means that the atmosphere already contains a good deal of condensed moisture. If the cooling should go on through the night, as it normally would, condensation would continue with rain as the likely result.

If, on the other hand, after the evening’s cooling has progressed and yet the colors near the horizon are prevailingly red it means that there is so little moisture in the atmosphere that the further increase due to the night’s condensation will not be sufficient to cause rain. Hence the natural delight of the sailor.

A gray morning sky implies an atmosphere full of water precisely as an evening gray does. The difference lies in the ensuing process. By morning the temperature has reached its lowest point and if this has not been sufficient to cause cooling to the rainpoint the chance for rain will be continually lessened by the growing heat of the rising sun. The gray, therefore, is the normal indication of a clear cool night which has permitted radiation and therefore condensation to this degree. It is for this reason that we have the heavy fogs of August and September followed by cloudless days.

A red morning sky shows, like the red evening sky, that condensation has not taken place to any extent. But this is abnormal for a clear night causes condensation. The red therefore means that a layer of heavy moist air above the surface levels has prevented the normal radiation. Hence when the day’s evaporation adds more moisture to that already at the higher levels the total humidity is likely to increase beyond the dewpoint with the resultant rain.

These two color auguries are among the most reliable of all the weather signs. Unfortunately the sunrises are scarcely ever on hand to be examined except by milkmen. But a careful scrutiny of the sunset will make one proficient in shades. In summer when the sun burns round and clear-cut and red on the rim of the horizon the air contains much dust and smoke, the accompaniment of dry weather. And as dry weather has a way of perpetuating itself such a sun makes dry and continued weather a safe prophecy. In winter the same red and flaming sun setting brilliant as new minted gold is a sure indication of clear and cold weather. In all seasons the light tints of the evening sky mean the atmosphere at its best. A golden sunset, a light breeze from the west, a glowing horizon as the sun goes down, slow fading colors all constitute a hundred to one bet for continued fair weather. The sunset colors that are surely followed by storm will be discussed in the next chapter.

The sky is too little regarded. Architects that do not consider the sky are behind in their calling. Maxfield Parrish has made himself famous by allying himself with its seas of color. The hunter can read it and learn whether he may sleep dry without his tent. Only we who shut ourselves within rooms and behind newspapers forget that there is a sky—until it falls and we are taken to a sanitarium.

From the night itself much may be discovered about the continuance of fair weather. A sky well sown with stars is a good sign. If only a few stars are visible the clear spell is about over. Stars twinkle because of abrupt variation in the temperature of the air strata. If the wind is from the west cold and clear will result no matter how much may twinkle twinkle little star. But if he twinkle with the wind from the south or east the cloud will soon fly. That is the way with these weather signs. One sign does not make a prophecy. It is the combination that has strength and reliability. Furthermore the eye must be trained by many comparisons.

Of all the conditions that make night forecasting easy the later evenings of the moon are the best. The moon furnishes just the proper amount of illumination to betray the air conditions. If she swims clear and triumphant well and good. If she rides bright while dark bellying clouds sweep over her in summer, inconsequential showers may follow. But if she disappears by faint degrees behind a thin but close knit curtain of cloud the clear weather is being definitely concluded.

A great many changes in the weather take place after three in the morning. Most campers are accustomed to waking anyway once or twice to replenish the fire, and a glance at the stars will show the sleepiest what changes are occurring in the eternal panorama. A man may have gone to bed in security to get up in a snowstorm, whereas a survey of the skies at three would have noted the coming change. The habit of waking in the dead of night,—which isn’t really so dead after all,—is not an unpleasant one. Its compensations are set forth in a beautiful and vivid chapter of Stewart Edward White’s “The Forest.” Every camper knows them, and this added mastery that a knowledge of the skies gives him lends a sense of power, which lasts until the unexpected happens.

For the unexpected happens to the best regulated of all forecasters, the Government. Equipped with every instrument and with an army whose business is nothing else than to hunt down storms and warn the public, the Weather Bureau is still surprised fifteen times out of a hundred by unforeseeable changes in atmospheric pressure. It is scarcely likely then that amateurs without flawless barometers and without reports of the current weather in three hundred places could hope to foretell with complete accuracy. But there is a place for the amateur, aside from his own personal gratification and profit. The Weather Bureau within the limits of the present appropriation cannot expect to predict for every village and borough. That the amateur may do and with as great accuracy for the few hours immediately in advance.

The Weather Bureau may predict with this large percentage of accuracy—85%—for forty-eight hours in advance because its scope is country wide. It may even forecast in a general way for seven days and still maintain a considerable advantage over almanac guesswork. But the man who is relying upon local signs is limited to ten or at most twelve hours. Of course he may guess beyond that but it is only a guess. The work that the Bureau does and that he may do within his limits is not guesswork. Meteorology is an exact science, and forecasting is an art. Both may be studied now in classes under professors with degrees in the same way that any other science and art may be studied. The old sort of weather wisdom which was a startling compound of wisdom, superstition, and inanity has passed away, or is passing away as rational weather talk spreads.

These limits of the layman—ten hours with no instruments—are further defined by his locality. In mountainous country changes come more quickly than in level localities, in winter than in summer, so that one’s prophetic time-limit is shortened.

While the best indications of the clear day are the great fundamental ones, there are many little signs that bolster up one’s confidence in one’s own predictions. The lessened humidity coincident with clear weather is responsible often for many little household prognostics. Salt is dry. The windows (of your summer cottage) do not stick. The children are less restless. Smoke ascends, or if the wind is blowing is not flattened to the ground. Flies are merely insects, for the time being, and not the devil. Swallows and the other birds that eat insects fly high because that is where the insects are. Spiders do not hesitate to make their webs on the lawn. They welcome dew but distrust rain. Cow and sheep feed quietly, rarely calling to one another as they do before a storm. In short the general aspect of these is normal and therefore remains unnoticed.

But all these household prognostics may be advertising the most placid weather while only twelve hours away and coming at sixty miles an hour may be the severest storm of the season. The Weather Bureau with its maps and barometers follows its every movement. The man in the woods whose comfort in summer and whose life in winter may depend upon his preparedness for the approaching storm does well to read its warnings and know its laws.

CHAPTER III

THE STORM CYCLE

Doubtless those who hope for a Hereafter of unmitigated ease and song, desire, on this earth, one long, sweet anticyclone. But theirs, in most of the United States, is disappointment. With an irregularity that seems perversely regular at times our fair weather is interrupted by a storm which in turn gives way to some more fair weather or another storm,—there is no telling which very long in advance. And that is why American weather ranks high among our speculative interests.

To emphasize this irregularity a seemingly regular succession of events may be noticed. It will cloud up, let’s say, on a Sunday, rain on Monday and Tuesday, clear on Wednesday, staying clear until Sunday when it will cloud up for the repeat. During this past season it rained on a dozen washdays in succession. The newspapers grew jocular about it. And very often one notices two or three rainy Sundays in a row. By actual observation this year we enjoyed fifteen clear Thursdays in succession in a normal spring.

The weather gets into a rut. And if the anticyclones and cyclones were all of the same intensity it is conceivable that the rainy Sundays might go on until the Day of Rest was changed by Statute. But the intensities of the whirls differ. Before long an anticyclone feebler than ordinary is overtaken by a cyclone and annihilated. Or one stronger than the average may dominate the situation for several days. Or the great body of cold air in winter over the interior of Canada may send a succession of moderate antis across our country making a barrier of dry cold air through which the lurking cyclone can not push.

Mostly, however, three days of anticyclonic influence and three days of cyclonic influence with one day in between for rest, the transition period, make up a normal week of it. Let the American farmer thank his stars (and clouds) for that. For no other regions of the earth are so consistently watered and sunned all the year round as the great expanse of the North American Continent.

The cyclone is that activity of the atmosphere which prevents us from suffering from an eternal drought. The cyclone is an accumulation of air which has become warmer than the air about it. This area of air usually has a central portion that is warmest of all. Since warmth expands, this air grows lighter and rises. Nature, steadfast in her grudge against a vacuum, causes the surrounding air to rush it. Since these contending currents cannot all occupy the central area at once they fall into a vast ascending spiral that spins faster and faster as it approaches the center. Imagine an inverted whirlpool. It is a replica on a much smaller scale of the great polar influx, except that the latter has a descending motion.

The cyclone thus is tails to the anticyclone’s heads, the reverse of the coin. Where the anti’s air was cool and dry the cyclone’s is warm and moist. The anti had a downward tendency and a motion, in our hemisphere, flowing outward from the apex in generous curves in the direction of clock hands. The cyclone has an upward tendency, flowing inward to the core contrariwise to clock hands.

From these two great actions and reactions come all the varieties of our weather. To understand the procession of the cyclones and anticyclones across our plateaus, our mountains, our plains, and our eastern highland is to know why, and often when, it will be clear or not. To mentally visualize the splendid sweep of the elements on their transcontinental run is to glimpse grandeur in the order of things which will go far to offset the petty annoyances of fog or sleet. Ignorance may be bliss, but knowledge is preparedness.

The anticyclone suggests a pyramid of cold, dry air. The cyclone suggests a shallow circular tank in leisurely whirl. But all comparisons are misleading and a caution is needed right here. For a storm is not a watering cart driven across our united skies by Jupiter Tonans Pluvius. It is NOT a receptacle from which rain drips until the supply is exhausted. A cyclone is a much more delicate operation than that. It is a process. It can renew itself and become a driving rain storm after it had all the appearance of being a sucked orange for a thousand miles.

Suppose that our cyclone, this organization of warm, moist air with its curving winds, enters the state of Washington on a Wednesday, from the North Pacific. As early as the Monday afternoon before the wind throughout all that section of the country would have shifted out of the west and have started to blow in some easterly direction,—northeast in British Columbia and southeast in lower Idaho. But since these winds are blowing from the interior they are dry, and consequently rain does not fall much before the storm center is near, that is on the Wednesday. If the storm center passes north of Tacoma the winds, shifting by south and southwest, bring in the ocean moisture and heavy rain commences which continues until the rising barometer and westerly winds indicate the approach of another anticyclone. So much for western Washington.

As the cyclone passes eastward it mounts the Cascades and its temperature is lowered, its moisture is squeezed out, and it stalks over Montana, the mere ghost of its former self, as far as energy and rainfall are concerned. To be sure it preserves its essential characteristics of relative warmth, and inwhirling winds. But let it continue. As its influence begins to be felt over Wisconsin and the Lake region the moister air is sucked into the whirl and rain, evaporated from Superior, falls on Minnesota. The east winds are the humid ones now, the west ones the dry. Eastward the center moves, over Indiana, Ohio, New York, the rainfall steadily increasing as the ocean reservoirs are tapped.

The first time you tell a New Englander that his easterly storms come from the west you are in danger, unless he be a child, for it is to the children that one may safely appeal. Indeed it is the increasing number of children who are learning these fundamental weather facts in the public schools that the Weather Bureau relies upon for a more intelligent support in the next generation. They teach their parents. These latter find it difficult to believe, however, that the storms which hurl the fishing fleets upon the coast in a blinding northeaster have not originated far out at sea, but have come across the continent. For the safe handling of boats knowledge of the rotary motion of storms is necessary that one may be able to tell by the direction of the winds and the way they are shifting where lies the center of the storm and its greatest intensity.

In Tacoma when the wind shifted by way of southeast, south, and southwest that was proof that the storm center was passing north of the city. Likewise if in New York the winds shift by way of northeast, north, and northwest the storm center is passing south of that city. As it drifts out to sea it is gradually dissipated by the changing influences on the North Atlantic. Very few of our storms ever reach Europe, although some have been traced to Siberia.

The Government has put its sleuths on the track of every storm that has crossed the United States in the last thirty years. These weather detectives with a thousand eyes have made diagrams of their actions, mapped their courses, computed their speeds, and if we don’t know where all our discarded storms go to, we at least know where most of them came from and how they acted when with us.

About a hundred and ten areas of low-pressure affect the country during the normal year. Of these all but seven, speaking in averages, come from the West so that the Boston mechanic who will not believe that the nor’easter comes via the Mississippi Valley is right about ⁷⁄110 of the time. But even that small fraction is no exception to the general law, because those seven storms are not born in Newfoundland but in our East Gulf States. They come up the Coast, and the wind blows from the northeast and north into their centers while they are still on the Carolina coast. The great hurricanes which are cradled in the tropics and march westward under the influence of the trades are genuine exceptions to the general westward rule, although they always eventually turn toward the east. They will be given the prominence they demand later, since the eastbound schedule must not be sidetracked now.

CIRRO-CUMULUS TO ALTO-STRATUS

Courtesy of Richard F. Warren

The wispy edges of the cloud at the brightest part are cirrus, the fleecy cloud at the extreme top is a thin alto-cumulus, and the dark base of the sky is stratus. But this stratus is too high for that classification and so they call it alto-stratus. This sky shows that the temperatures are moderate, a cold sky being much better packed, and a warm one fluffier. The fact that a veil of cirrus has not preceded the heavier clouds argues that the coming storm will not be of much consequence. This sort of cloud bank arising after a period of cold weather is the best possible prediction of a thaw. Slight rain might follow within a few hours.

Three cyclones a year form over the lower Ohio River basin. On account of their origin over land instead of over water they rarely acquire much energy. Once in a decade such depressions deepen rapidly. It was one of these Ohio River storms that increased greatly in energy while moving from West Virginia to the Jersey Coast that gave Philadelphia her Christmas Blizzard, a surprise to her citizens and to the Weather Bureau, for most of the snow fell with the mercury above freezing. The flare-back which gave Taft his big inaugural snowstorm is another example of the way a depression may deepen on approaching the coast. Until the upper atmosphere is as well understood and watched as the lower, or until instruments are perfected whereby the weather conditions can be made self-announcing such surprises are absolutely unavoidable. Under conditions that warrant any suspicion of sudden developments the Bureau at Washington is careful to order extra observations in the areas likely to be affected, but no surface observations can quite suffice.

Fifteen storms a year originate over the west Gulf States, or, drifting in from the Pacific over Arizona and New Mexico begin to acquire energy in Texas. Twelve are set up over the Colorado mountains. These usually dip down into Texas before starting their drive toward the northeast. After both these sets of storms get under way they strike resolutely for the same locality,—the St. Lawrence Valley. The conformation of the St. Lawrence region provides an irresistible attraction for American storms. Occasionally a very strong anticyclone holds that territory and pushes the cyclone off the coast at Hatteras or even makes them drift across the country to Florida. But such occasions are exceptional. Give the ordinary cyclone its head, and, ten to one, you will find it on the way to the St. Lawrence. The inhabitants will confirm this statement, I am sure. They do not feel discriminated against in the matter of weather. They get nearly everything that is going. Since they have to accommodate from seventy to eighty cyclones in fifty-two weeks they have very little time to brood over any one variety of weather. With the optimism of that section of the country they say, “If you don’t like our weather, wait a minute.”

Ten storms a year originate over the Rocky Mountain Plateau, north of Colorado. About twenty cross over from the Canadian Provinces of Alberta and British Columbia. And all our other storms, about forty each year, enter our country from the North Pacific by way of Washington and Oregon. Many of these drift across the northern tier of states without any great display of energy, at least before they reach the Lake region. But the majority loop down somewhat into the middle west as far south as Kansas, and then make their turn toward the inevitable St. Lawrence. They usually require four days to make the trip from coast to coast by this route, as also by the more direct northern route, because on that they travel more at leisure. But the storms from Texas, whose energy is greatest because of greater heat and moisture, occasionally speed from Oklahoma to New York in thirty-six hours.

In summer all speeds are reduced. This is because the disparities in temperature are less. In winter where greater extremes of temperature are brought into conjunction the processes of the storm are all more violent. And it is a bit disheartening to know that a storm is aggravated to even greater endeavors by its own exertions. Its energy provides the conditions to stimulate greater energy, and, like a fire, it increases as it goes. If it did not run out of the zone which nourished it and proceed into another zone where conditions were distinctly discouraging the limits of the storm would be much extended, and vast territories would be devastated by the self-propelling combination of wind and water.

To the generality of us the word storm means rain. To the scientist it means wind. In reality the cyclone is rare that crosses our country without causing rain somewhere along its track. The curiosity of the Weather Bureau to find out the paths of the storm centers is abundantly justified because it is along these paths that the heaviest rainfall and the severest winds occur. But whether or not there is precipitation on the path of the cyclone it is rated as a storm if there is a lowering of pressure and consequent wind-shift.

The storm centers are not always well-defined, and quite often the circulation of the wind about them is not complete. Such cyclones never amount to much, although there is always the possibility of their closing in and developing a complete circulation with the attendant increase of energy. The incomplete cyclones over the desert and plateau regions are lame affairs, lacking interest and advancing timidly if at all. But once let them drift into a locality where they can be supplied with moist air, they pick up energy, keep a definite course, and advance with increasing speed.

Very often the center will split up, the circulation perfecting itself around both centers of depression. One of these will likely be over Minnesota and the other over Texas and the organization will steam-roller the states to the east in the manner of a gigantic dumb-bell. This formation is more likely to have been caused by the two centers appearing simultaneously than by a split in an original center. The weather reports call this fashion of storm a trough of low pressure. The southern center is the one that develops the more energy on its turn to the northeast. If the two centers should unite on reaching the northeast a very heavy precipitation is the invariable result.

All cyclones have much greater length than breadth. They frequently stretch from unknown latitudes in Canada into unrecorded distances into the Gulf, while on the other hand it is a very large storm that rains simultaneously upon the Mississippi and the Atlantic. Behind a cyclone of pronounced energy a second whirl, called a secondary depression, often develops, in which case the period of wet weather is prolonged. Also, more rarely, an offshoot forms ahead of the main depression.

A sluggish, sulky cyclone either in winter or summer provides more opportunity to humanity for self-discipline than almost any other feature of our national environment. In winter when the depression slows up it settles down upon one community in the guise of fog, and stays by the locality until an anticyclone blows in and noses it out. Fog is aggravation, but a hot wave is suffering and the hot wave is caused by a depression weak in character but generous in dimensions getting held up on the northern half of our country. By its nature it attracts the air from all sides, and being in the north, the direction of the wind over most of the country would be southerly. Air from the west and north has a downward tendency, but south and east winds are surface currents. Consequently these winds, blowing over leagues of heated soil, become dry and parching. If the depression lingers long the entire country to the east, south, and west soon suffers from superheated air. At last the very intensity of the heat defeats itself and the reaction to cooler is effected dramatically through a thunderstorm.

The well-developed cyclone in winter causes what we all know as a three days’ rain, although continuous precipitation rarely lasts over ten hours. The rest of the time is occupied by general cloudiness with occasional sprinkles and a final downpour as the wind shifts to the west and the anticyclone nears. In summer the depressions, being shallower, rarely cause continuous cloudiness for three days, although their influence often lasts as long as that in the guise of a series of thunderstorms. The line of storms extends several hundred miles, bombarding all the towns from Albany to Richmond. These thunderstorms sometimes achieve in an hour or two even greater results than their winter relatives can accomplish in three days in the matter of rainfall, wind velocity, and general destructiveness. Our wettest months are July and August and not December and January.

The freedom of the wind has been the subject of much poetic and prosaic license. As a matter of fact the wind is the veriest slave of all the elements. It is harried about from cyclone to anticyclone, wound up in tornadoes, directed hither and thither by changing temperatures. It blows, not where it listeth, but where it has to. And circuitously at that. For once the path of duty is not straight. That is another fact that the Boston mechanic would have been slow to accept,—that the wind blows in curves. A little consideration, however, of the fact that the wind is perpetually unwinding in great curves from the anticyclone and winding up on the cyclone will show that nowhere can it be blowing in a perfectly straight line.

Thus it becomes the surest indication that a cyclone is to the west of one if the wind blows from an easterly point. The storm is bound to move toward the east, therefore the rapidity with which the clouds move and thicken will signify when the area of precipitation will reach the observer. The cycle of the storm is normally this: After a cloudless and windless night a light air springs up from a little north of east. At the same time strands of thin wavy clouds appear, very high up. They may be seen to be moving from the southwest or northwest. Their velocity is great. Their name is cirrus, and they are called mares’ tails by the sailors. They are followed by several hours of clear skies, usually; but if the storm is smaller and close at hand there is no clear interval.

Before the larger storms these cirrus clouds are sent up as storm signals twenty-four and even forty-eight hours in advance. The day that intervenes is very clear, the air feels softer, the temperature is higher. In midafternoon more cirrus appears, and as condensation follows the quick cooling the silky lines increase in number. Beneath them a thicker formation, known as cirro-stratus, forms a dense bank in the west and southwest. The sun sets in a gray obscurity. If there is a moon it fades by degrees behind the veil of alto-stratus, and the halo which first was seen wide enough to enclose several stars narrows until it chokes the moon in its ever-thickening cocoon of vapor.

There is no value whatever in the old superstition that the number of stars within the halo foretells the number of days that it will rain or snow. The same halo that encloses three stars at eight o’clock may have narrowed down to one by midnight, or none at all, so that the prophetic circle is bound in the very nature of its increase to contradict itself. The presence of a halo is a pretty sure sign of some precipitation within twenty-four or thirty hours. It fails about thirteen times in a hundred. If the halo is observed around the sun it is an even surer sign, failing only seven times the hundred.

During the time of cloud-increase the wind will probably lull before a snow, so that the hour or so before precipitation begins is one of intense brooding calm. Or if there is no calm the wind, now easterly, will be very gentle. Soon after the precipitation begins the wind will begin to freshen and will continue to increase in velocity until the center of the storm is close to the locality. This will require about eight hours for the average storm. As storms vary an average is a very misleading thing and the best way to judge of the length and severity of the storm is by watching the wind. If it increases gradually the storm will be of long duration. If the wind rises fitfully and swiftly it will not likely be long but may be severe. If the wind reaches any considerable velocity before the rain or snow begins the storm is sure to be short and severe.

The color and formation of the clouds will tell when the precipitation is about to begin. In summer, no matter how striking and black are the shapes and shadows of the clouds, rain will not fall until a gray patch, a uniform veil called nimbus is seen. In the little showers of April this patch of unicolored cloud is there, as well as behind the great arch of the onrushing thunderstorm. In winter raindrops are smaller and the tendency of the clouds is to appear a dull, uniform gray at all times. But the careful observer can detect a difference between the nature of the clouds several hours before precipitation and their color immediately before.

When snow is about to fall no seams are visible. An impenetrable film obscures all the joints. From such a sky as this snow is sure to fall. But if seams are visible, if parts of the skyscape are darker than others, then, no matter whether the temperature on the ground is below freezing a rain storm will ensue. Very often these winter rains begin in snow or sleet, but the clouds register the moment when the change from snow to rain is to be made. The presence of swift-flying low clouds from the east is a certain sign that the change to a temperature above freezing has been effected in the upper strata of the atmosphere. This variety of cloud is called scud, and accompanies rain and wind rather than foretelling it long in advance.

If the storm is approaching from the southwest the precipitation begins near the coast about twelve hours after the cirrus clouds commence to thicken and about twenty-four after they were first seen. In some localities as much as thirty-six and even forty-eight hours are sometimes required for the east wind to bring the humidity to the dew-point. Just a little observation will enable one to gauge the ordinary length of time required to bring things to the rain-pitch in one’s own country. Of course no two storms in succession make the trip under the same auspices and with the same speed. The sign of the Universe should be a pendulum. One period of cyclone, anticyclone, cyclone will traverse the country rapidly. Then there will be a halt all along the line, and the next series,—anticyclone, cyclone, anticyclone, will take three days longer to make the crossing. Otherwise our weather would have a deadening regularity.

On an average our storms cross the country at the rate of about six hundred miles a day. This is the average. Some delay, linger, and wait for days over one locality. Others do a thousand miles in the twenty-four hours. They thicken up enough to cause rain from two hundred to six hundred miles in advance of their centers. It stops raining not long after the actual center has passed.

But for picnic purposes the storm is far from being over. For even though continuous raining has stopped the low pressure still induces a degenerate sort of precipitation called showers, or oftener mist for another twelve hours (usually in winter). Then as the cooling influence of the anticyclone approaches the rain recommences. This time it is not for long, however, and is followed by permanent clearing, the wind shifting into the west. Sometimes the change to blue sky is abrupt. But if the subsequent anticyclone is not very well defined, cloudy conditions may linger for a couple of days. Such clouds are usually much broken and show white at the edges and never cause more than a chilly feeling.

This attempt to outline the customary cycle of the storm,—clear sky, cirrus cloud, wind-shift to the east, the denser cirro-stratus, the pavement-like stratus, the woolly nimbus, the first continuous hours of rain, the misty interval, the windshift to the west, the final shower, and breaking cloud, the all-blue sky—this storm-schedule is always subject to change. But the fundamentals are there in disguise every time. They only have to be looked for and there is some satisfaction in penetrating the disguise.

When a storm comes up the Atlantic Coast, as happens a few times a winter, the process is shortened, because the effects of the larger easterly quadrants are felt only at sea. The most prominent recent illustration of this type of storm was the severe snowstorm that swept the coast states from Carolina to Maine the Saturday before Easter, 1915. Its calendar read as follows: Friday, 8 P. M., cirrus clouds thickening into cirro-stratus. Midnight, stars faintly visible, wind from northeast, 12 miles an hour. Sunrise, stratus clouds, wind rising in gusts at Philadelphia to 30 miles; 8 A. M., rapid consolidation of clouds with snow shortly after, although the temperature at the surface of the earth was as high as seven degrees above the freezing point. This rapidly dropped to freezing. Flakes were irregular in size. Until one o’clock in the afternoon the snow thickened with gusts of wind up to forty miles. Snowfall for five hours was 14 inches, an unprecedented fall for this locality.

Then the storm waned for five hours more, 5 inches more of snow falling. Precipitation practically ceased at 6 P. M. By sunrise on Sunday the skies were free of clouds and the wind blew gently from the northwest.

Occasionally a high pressure area out at sea and beyond the ken of the Weather Bureau causes one of these coast storms to curve inward to the surprise of everybody. Occasionally, too, the transcontinental storms are driven north or south of their accustomed paths. While the divergence may be slight, it causes a margin of variance from the accuracy of the Bureau’s report. Then arises a second storm,—one of indignation—from all the people on one side of the strip who carried umbrellas to no purpose, and from the others,—who didn’t.

This pushing aside of the cyclone is caused by pressure variation that only hourly reports from many localities could detect. Vast hidden influences shift the weights ever so little and the meteorological express is wrecked. But this happens, at most, fifteen times in a hundred, and remembering the unseen agencies to be coped with people are refraining more and more from the tart criticisms of former times, not in charity but in justice, although there is small tendency yet to forward eulogies to the Bureau in recognition of the eighty-five times it is right.

CHAPTER IV

SKY SIGNS FOR CAMPERS

The weather-wise, even more so than poets, are born. But that only goes to say that weather-wisdom can be fathered. For poetry and canoeing and the art of making fires, once the desire for these things is born, may be aided infinitely by observation and practice. Nobody can teach a man the smell of the wind. But the chap who feels nature beating under his heart can, by taking thought, add anything to his stature. So it is with those who are called weather-wise. An unconscious desire, a little conscious knowledge, a good deal of experimentation with the cycle of days, and you have a weatherman.

These chapters aim to put the little conscious knowledge into the hands of the people with the unconscious desire, so that when they take their week in the woods for the first time (and their month for the second time) they may enjoy the shifting scenery of the sky-ocean and, incidentally, a dry skin. For I take it that everybody will soon be camping. Maine and the Adirondacks have become a family barracks. It is Hudson Bay for bachelors. And over this expanse of woods and children the weather problem ranks with the domestic one. For naturally if a soaking would endanger his vacation the husband must not permit a rain,—unexpectedly. In all seriousness, it is of avail to know the skies if one is going into the wilds just as it is of avail to know what severed arteries demand, what woods burn well, and what mushrooms can be eaten, even though one can get along without knowing these things until perchance the artery is severed or the arched squall catches one far from shore.

At the very least, one grain of weather wisdom prevents a mush of discomfort. And if, fellow-camper, the following observations gathered on a thousand thoughtless walks do not tally (for the northeastern states) with yours, write me, so that in the end we may finally contrive together a completer handbook of our weather.

THE CLOUDS

Clouds are signposts on the highway of the winds. Every phase of the weather, except stark clearness, is commented upon by a cloud of some sort. When danger is close they thicken. When it passes they disappear. The aviators of the future will be cloud-wary. He who flies must read or never fly again.

The cirrus cloud is always the first to appear in the series that leads up to the storm. It looks like the tail of Pegasus and for it the old forecasters in their forecastles made a special proverb.

“Mackerel scales and mares’ tails
Make lofty ships carry low sails.”

These white plumes and scrolls which are in reality glistening ice-breath, fly at the height of five, six, seven, and even eight miles. And as a sign of coming storm they are about as infallible as anything may be in this erratic world. They were born in the cradle of a storm. The storm center was breathing warmed air upward to great heights, and although the disc of the storm itself was only two or three miles deep, its nucleus, crater-like, shot warm columns twice as far. With just enough moisture content to make a showing against the blue these streamers flowed to the eastward. At those dizzy heights the prevailing westerlies are in full force, blowing from eighty to two hundred miles an hour night after night and day after day. These westerlies caught the storm exhalations, the streamers, and hurled them eastward at greater speed than the main body of the storm. And that is the reason that we see these cirrus clouds always eight, mostly twelve, often twenty-four and sometimes forty-eight hours before the storm is due.

Just a few strands of cirrus have little significance. They may be condensation from a local disturbance, or a back fling from a past storm. But if the procession of the cirri has some continuity and broadens to the western horizon it is a sign about eight times in ten that a cyclone is approaching. Occasionally the storm center is too far to the south or north to cause rains at your locality, but the cirri bank up on the horizon and their lacework covers the sky. If they appear to be moving toward the region of greatest cloudiness it is not a sign of precipitation. This condition is most apparent at Philadelphia when the storm center over Alabama or Mississippi floats out to sea by way of Florida without having the energy to turn north. Then the cirrus is seen thickly on our southern horizon. Looking closely one sees that the cirri are moving from the northwest, and are being drawn into the storm area instead of proceeding in advance of it.

Careful watching will sometimes enable one to tell whether the tails are increasing or decreasing in size. If they dissolve it means that the cyclone from which they were projected is losing strength because of new conditions. Cloudiness may follow but no precipitation of consequence. The plumy tails are expressive: pointing upward they mean that the upward currents are strong and rain will follow; pointing downward they mean that the cold dry upper currents have the greater weight and clear weather is likely. In summer the cirrus cloud formations are not such certain advance agents of rain because all depressions are weaker and less able to confront a well-intrenched drought. As the proverb goes, “all signs of rain fail in dry weather,” and there is some truth in it.

The fine wavy cirrus clouds often increase in number, develop in texture until the blue sky has become veiled with a muslin-like layer of mist. This is the cirro-stratus, and is a development of the cirrus, but it does not fly so high. Its significance is of greater humidity and is the first real confirmation of the earlier promise of the cirri. Another form that the cirro stratus may assume is the mackerel sky,—clouds with the light and shade of the scales of a fish. If this formation is well-defined and following cirrus it is a fairly accurate storm indicator. It is not quite infallible, however, as the same forms may be assumed when the process is from wet to dry.

The old proverb, “Mackerel sky, soon wet or soon dry,” expresses this uncertainty. If dry is to follow the scales will appreciably lessen in size and perhaps disappear. If the cirro-stratus or scaly clouds are followed by a conspicuous lowering it is only a question of a few hours until precipitation begins. The cirro-stratus at a lower level is called alto-stratus and this becomes heavy enough to obscure the sun.

The cloud process from stratus on is slow or rapid, depending upon the energy of the coming storm and the rate of its approach. In most cases the clouds darken, solidify, and become a uniform gray, no shadows thrown, no joints. Soon after the leaden hues are thus seamless the first snowflake falls. If it doesn’t it is a sign that the process of condensation is halting: the storm will not be severe. Sometimes there is no precipitation after all this preparation, but under these circumstances the wind has not ventured much east of north. From the time that the snow starts the clouds have chance to tell little. Only by a process of relative lightening or darkening can the progress of the storm be followed and the wind, and not the clouds at all, is the factor to be watched; for occasionally the sun may shine through the tenuous snowclouds without presaging any genuine clearing so long as the wind is in the east.

But in summer the clouds become even more eloquent than the wind. The rain-cloud, called the nimbus, becomes different from the dull winter spectacle. In summer air becomes heated much more quickly and the warm currents pour up into the cold altitudes where they condense into the marvelous Mont Blancs (or ice-cream cones) of a summer afternoon. These piled masses of vapor are cumulus clouds, and if they don’t overdo the matter are a sign of fair weather. They should appear as little cottony puffs about ten or eleven in the morning, increase slowly in size, rear their dazzling heads and then start to melt about four in the afternoon.

But perhaps the upward rush of warm, moist air has been so great in the morning that the afternoon cooling cannot dispose of it all without spilling. Then occurs a little shower,—the April sort. Often in our mountainous districts it showers every day for this reason. The great thunderstorms come for greater reasons: they are yoked to a low pressure area and represent the summer’s brother to the winter’s three-day storm.

Cumulus clouds are called fair weather clouds until their bellies swell and blacken and they begin to form a combination in restraint of sunlight. Even then it will not rain so much out of the blackness as out of the grayness behind it, and if there is no grayness chances are that you will escape a wetting. One can almost always measure the amount of rain that is imminent by the density of the curtain being let down from the rear of the cloud. If you can see the other clouds through it or the landscape the shower will be slight. If a gray curtain obscures everything behind it you had better pull your canoe out of the water and hide under it if time is less valuable than a dry skin. Such showers may be successive but rarely continuous.

Rain clouds have been observed within 230 yards of the ground. Very often it can be seen to rain from lofty clouds and the fringe of moisture apparently fail to reach the earth, because the condensation was licked up and totally absorbed on entering a stratum of warmer air. The reverse of this occurs on rare occasions;—condensation takes place so rapidly that a cloud does not have time to form, and rain comes from an apparently clear sky. This phenomenon has been witnessed oftenest in dry regions and never for very long or in great amounts, although a half hour of this sort of disembodied storm is on record.

If the cumulus clouds of the summer’s afternoon do not decrease in size as evening approaches showers may be looked for during the night. And if the morning sky is full of these puffy little clouds the day’s evaporation on adding to them will probably cause rain. A trained eye will distinguish between a stale and fresh appearance in cloud formation, the light, newly made, fresh clouds, like fresh bread, contain more moisture. If the clouds have much white about them they need not be feared as rain-bearers. Clouds are much higher in summer than in winter and the raindrops of warm air are larger than those of cool.

If cumulus clouds heap up to leeward, that is, to the north, or northwest on a south or southwest wind a heavy storm is sure to follow. This is notably so as regards the series of showers in connection with the passage of a low-pressure area. The wind will bear heavy showers from the south (in summer) for a whole morning and half the afternoon with intervals of brilliant sky and burning sun. Or perhaps the south wind will not produce showers, but all the time along the northwest horizon a bank of cloud grows blacker and approaches the zenith, flying in the face of the wind or tacking like a squadron against it. About the time that the lightning becomes noticeable and the thunder is heard the wind drops suddenly, veers into the west, and the face of things darkens with the onrush of the tempest.

Although no rain may have fallen while the wind was in the southern quarter yet that constituted the first half of the storm and the onslaught of rain and thunder the second. While the storm area moved from the west to the east the circulation of air about the center was vividly demonstrated by the south wind blowing into the depression, whose center was epitomized by the moment of calm before the charge of the plumed thunderheads from the northwest.

Most camping is done either in hilly or mountainous country where the movement of clouds is swifter and more changeable than over flat lands. There is one sign of great reliability: if the mountains put on their nightcaps the weather is changing for the wetter, and if clouds rise on the slopes of the hills or up ravines, or increase their height noticeably over the mountain-tops, the weather is changing for the dryer. In the mountains where abrupt cliffs toss the winds with all their moisture to heights that cool clouds form and condense rapidly and the weather changes quickly. But even in the mountains the big changes give plenty of warning.

Often clouds may be noticed moving in two or even three directions on different levels at once. The upper stratum will probably be cirrus from the west. Cumulus or stratus may be floating up from the south. A light drift of vapor called scud may fly on the surface easterly wind. Such a confused condition of wind circulation betokens an unsettled system of air pressures and as frequent collisions of the air bodies at varying temperatures are inevitable rains, probably heavy, will follow.

On clear days one will be surprised to see isolated clouds, usually the torn, thin sort, drifting across the sky from the east. A change will follow soon.

In winter black, hard clouds betoken a bleak wind.

Clear winter days several times a season show a brilliant blue sky filling with great cumulus clouds of dark blue, blurred at the top and gray at the base. They will sprinkle snow in smart, short flurries, and are ushering in a period of clear and much colder weather.

A sky full of white clouds and much light is a cheerful sign of continuing fair weather.

The softer the sky the milder the weather and the more gentle the wind. It is the dark gloomy blues that bring the wind. But do not mistake the woolly softness of the rolling clouds before a thunderstorm. A sudden and often violent gust follows. Tumbling clouds in any event should make one wary of venturing on water. Summer drownings would not be so numerous if the portent of the squall were heeded.

To this data might be added many singular cloud formations that are not observed often. The funnel shaped cloud of the tornado, the green shades of the hurricane cloud, the green sky of cold weather showing out between layers of steel blue, coppery tints that show before heavy storms sometimes, variations of color at sunset each of which has a meaning which practice in deciphering will make clear. But enough has been given to show sky-searchers how many are the tips of coming weather that may be read from a conglomeration of fog particles. Nobody with eyes should be caught unawares by day. The look of the sunset shadows forth much of the coming night. And throughout all this truth holds: the greater the coming storm the longer and clearer are the warnings given to the watchful.

THE WINDS

The wind is the ring-master of the clouds. It whistles and they obey. Therefore to be windwise is to be weatherwise, almost.

One can get a hold on the wind by learning to gauge its strength. Look at the trees or the smoke from your city chimneys and guess how fast it blows at eight o’clock in the morning, or eight at night. The weather report the next day will tell you how nearly you were right.

Beginning is easy; anybody can guess a calm. When the leaves are just moving lazily the Weather Bureau calls it a light or gentle breeze, moving from 2 to 5 miles an hour. A fresh breeze, from 6 to 15 miles will stir the twigs at first and finally swing the branches about. From 16 to 25 miles, a brisk wind, will cause white caps on the lakes, tossing the tops of the trees, but breaking only small twigs. Increasing from 26 to 40 miles it becomes a high wind that breaks branches on trees, wrecks signs in the towns, causes high waves at sea and roars like the ocean in heavy squalls through the woods. From 40 to 60 miles an hour makes a gale. Sailing craft are now in danger. The pressure at 50 miles an hour is 13 pounds to the square foot, having risen from three-quarters of an ounce at 3 miles. This pressure becomes 40 pounds per foot when the wind reaches a velocity of 90 miles.

At 60 trees are uprooted, chimneys may go, it is difficult to walk against, the noise becomes very great but rather inspires than frightens. As the gale increases from 60 to 80 (which velocity the Bureau rather weakly calls a storm wind), danger rapidly increases. Trees are prostrated, the uproar becomes terrifying, walking without aid is impossible, the great ocean liners are in danger, the sea becomes a whitened surface of driving spume that heaps up into piles of water thirty or more feet high, windows are blown in and frame houses cannot stand much greater velocities. Anything from 80 miles an hour up is well called a hurricane. Everything goes at 100. At Galveston the machine that registered the wind velocity blew away at 100.

They have better instruments now, and in many places velocities of over a hundred miles an hour have been recorded. As high as 186 miles was registered on the top of Mt. Washington, and in a single gust 110 at Montreal. The great hurricane winds are most felt at a few of the exposed places on our coasts. Cape Mendocino, on the Pacific, has 144 miles an hour to its credit in a January hurricane. But enough destruction is done at 90 miles. Fields are stripped of their crops, or leveled; houses are demolished unless they are specially built, like the New York sky-scrapers, to withstand much higher velocities. In the small whirling storms called tornadoes the wind is estimated to reach a velocity of 200 to 500 miles, and nothing but the cyclone cellar will shelter one from the fury of the elements when they are really unleashed.

The higher one goes the greater the velocity of the wind. On the top of Mt. Washington 100 miles is rather common for hours at a time and 150 is recorded now and then. That is only 6000 feet above Boston. If such a force struck Boston for a minute it would be blown en masse into the Bay.

Velocities on land are less than those at sea, because of the resulting friction from obstacles. Velocities in summer are lower (thunder gusts excepted) than in winter. Since the wind is caused by differences in atmospheric pressure, and that in turn by disparities in temperature, winter holds the palm for greater velocities because the wide whirl of a cyclone over the great plains may cause to mix air from Texas with a temperature of 60 degrees with air from Montana of 30 degrees below zero, while the summer temperatures in both states might easily be 80 degrees.

Throughout most of our land certain winds have always the same bearing upon the weather and this correspondence is roughly the same over most of the country. West winds, for instance, are an almost universal guarantee of clear weather. The Pacific Coast and western Florida are the exceptions.

Northwest winds bring clear skies and cool weather everywhere. In winter in the north plateau section heavy snows arrive in advance of the severe cold waves that come on these northwest gales.

North winds are the cold bearing ones. Clear skies prevail under their influence.

Northeast winds are cold, raw snow-bearing winds in winter and spring and bring chilly rains in midsummer.

East winds are the surest rainbringers of all for the eastern two-thirds of the country, and are soon followed by rain with a shift of wind over the other third. Their temperatures are more moderate than those of the northeast storms.

The greatest falls of rain occur, however, with the southeast winds, whose moisture content is greater than that of the others because they are warmer and blow off water except in Rocky Mountain districts.

South winds are warm and contain much moisture, which falls in showers rather than in continuous rains.

The southwest winds of winter precede a thaw and are much damper than west winds. In summer over much of our country they are hot, parching winds that injure vegetation.

The average velocity of the wind from these different quarters is variable in different parts of the country, the severest being on the southeast and northwest quadrants. The highest winds are always where the steepest gradients are; that is, where the barometric pressure decreases or increases the fastest. The steepest gradients are usually on the northeast and northwest sides of the storm center, with the exception of the Atlantic Coast where the southeast winds are often highest. The average for the northeast quadrant is 16 miles, for S. E. 30, for S. W. 20, and for the N. W. 30 miles an hour. But averages can deceive. As a matter of fact single instances of great wind velocities occur from each point of the compass. The greatest velocity ever recorded at Philadelphia occurred in October, 1878, when the wind blew seventy-five miles an hour from the southeast. But the record velocities for eight of the other months were registered in the northwest quadrant.

ALTO-STRATUS

Courtesy of Richard F. Warren

Not so high as cirro-stratus, and yet partaking of the same skeiny texture. This would be a normal sky in winter about six hours after the veil of cirrus had begun to throw its haze about the sun. No other cloud formations appear, however, and so the area of precipitation is still pretty far away. In summer such a sky is less common. If the disturbance is to amount to anything the cirro-cumulus will soon form. If the wind is from a westerly quarter the blanket of cloud is doubtless a drift from some distant storm, which will not affect this locality. The wind is always blowing toward a storm and away from clear weather.

The period of time when the barometer is beginning to rise after having been very low is that when the strongest winds blow.

Some sections of our country have special kinds of wind that are peculiarly their own, notably Colorado, Wyoming, and Montana where the chinook reigns. This phenomenon belongs only to the cold season and only to the coldest days of it. It is a warm wind that begins to blow without much warning from the southern quarter. It is caused by a body of cold air suddenly falling from a great height. As it falls its descent heats it and it causes a rise in the temperature of the surrounding locality that greatly exceeds any rise from other causes. The increase in temperature will be as much as forty degrees in fifteen minutes.

This sudden dry heat is a great snow-eater. If it were not for the chinook the snow-blanket would stay so much longer on the cattle ranges that they would be useless as such. In northeastern sections of our country and Canada the warm winds blowing in from the ocean at the approach of a cyclone do away with the snow rapidly but with nothing like the speed of the chinook.

Another phenomenon of the air that is of tremendous benefit to man is the sea-breeze. During the intense heat of a hot wave the wind may shift to the east in Boston and in fifteen minutes coats are comfortable. Such a shift may bring relief to a strip of land two hundred miles wide along our entire eastern seaboard. The sea-breeze is explained by the fact that the land cools more quickly than the sea and also warms more easily. During the whole forenoon of a summer’s day the sun has been pouring upon land and sea, but the land-air has become much hotter than the air over the sea. It rises and the sea-air rushes landward. By midnight the land has cooled off even more than the sea and the heavier air now presses out to sea again. On every normal day this balancing process takes place.

If it doesn’t conditions are abnormal and chances are that mischief is brewing. This ebb and flow of warmer and cooler air is, on a small scale, exactly what is happening on a vastly larger field of operations between cyclone and anticyclone. And it is the dominance of the anticyclone with its prolonged rush of air from the northwest that interrupts the sea breeze for two or three days in winter, as the cyclone prevents the night land breeze from taking place when it is central off the eastern coast.

The exchange of air between mountain side and valley is similar to the land-and-sea breeze. The rarer air on the mountain side heats faster by day and cools faster by night than the denser air in the valley. Therefore during the day it rises and the valley air rushes up to take its place; during the night it cools and sinks into the valley. This is a great help when one is shut up in a secluded valley for several days and cannot get a good view of the skies. The atmosphere is acting properly and will remain settled so long as the air blows up your ravine for most of the day, and turns about sundown and blows out and down the ravine like a flood of refreshing water.

Of course many valleys are so large as to be affected, not by these local causes, but by the larger movements of the anticyclones when the sure-clear west wind may blow up the valley for three days at a time. But, nevertheless, for most mountainous places the logic holds and you may expect rain if the wind does not blow coolly down the ravine at night. Of course watch your clouds for confirmation.

In times of calm prepare for storm. An eminent meteorologist has frowned upon me for saying that. It is not the whole truth, I admit, but there is a certain kind of calm which happens often enough to justify the remark. It happens this way. A severe storm has passed. The customary anticyclone with its brisk northwest winds has arrived and is blowing with all the vigor necessary to induce one to believe that the clear weather is to continue for the usual length of time; that is, three or four days. But suddenly in the early afternoon, just when it should be blowing its hardest, the wind drops, lulls, shows a tendency to change its direction. There is only one explanation. Another cyclone has developed off in the west. It has knocked the anticyclone on the flank, taken the teeth out of the gale.

The wind shows this before clouds can. The absence of wind when there ought to be a lot shows it before even the first cirrus swims overhead. The chance is that when the flow of anticyclonic air has been thus rudely cut off and stillness follows, it will be storming by morning. It is best to keep an eye on these abnormal, precipitous calms. In times of peace prepare for rain.

But the eminent meteorologist was eminently right when he said that the statement was misleading unless explained. For there are many kinds of calms that do not portend coming storms. Nearly every day, winter and summer, but particularly in summer, the wind drops to a calm at sunset. That is a time of adjustment. After sunset when the accounts are all in the wind springs up with as much force as it had in the afternoon and continues until dawn. At sunrise, however, there is another truce. If this truce is neglected either at sunrise or at sunset it is a sign that either a cyclone on an anticyclone is very much in the ascendency. These truces are most often observed at the seashore when you are out sailing and the smell of supper fills your nostrils but is not sufficient to fill your sails. These calms are normal and the best sign of a fair day on the morrow, provided the other signs agree.

During the great transition period from summer to winter comes that autumnal truce, Indian Summer, which is the chief claim to fame of American weather. For day after day a brooding haze sleeps in the air, sometimes for weeks there is no wind of any strength. Winter advances insidiously in the fall but retreats in commotion, and the cooling off process permits of these still days while they are uncommon in the spring. The wind checks off more mileage in March than in any other month.

While the regular day’s end calm and the calm of the year’s exhaustion mean continued fair weather, there is one calm that everybody knows, which is the most dramatic moment in the whole repertory of the weather: the foreboding, ten-count wait before the knockout blow of the thunderstorm. But when that calm comes every one is already sitting tight so that it is not much account as a warning. They say that the intense stillness before the hurricane strikes is uncanny.

Whether inshore or afloat the wind is to be watched if you would know what weather is to be. It is only another of Nature’s paradoxes that the most unstable element should be the most reliable guide of all on the uncertain trail of the next day’s weather.

TEMPERATURES

Considering that the temperature of the sun is 14,072 degrees Fahrenheit and the temperature of space is absolute zero, 459 degrees below ours, we do very well on earth to be as comfortable as we are.

And we owe it all to the atmosphere which keeps the sun from concentrating upon us. Our place in the sun is so very small that we intercept only one-half of one billionth of the heat which it is giving off night and day. But that is sufficient to do a lot of damage if it could get at us.

But even the paltry range of temperatures so far recorded on our planet,—from 134 degrees above zero one day in California, to 90 degrees below zero one night in Siberia,—is by no means a fair statement of the extremes we are called upon to bear. Only twice a decade in our country does the mercury vary as much as sixty degrees in twenty-four hours, and there are vast areas where the daily change amounts to only a few degrees.

The changes that do come so suddenly to us, particularly in winter and that are known as cold waves, are in reality beneficial. To them we Americans may owe our energy, our vivacity, our changeability of mood. The refrigerated, revivified air sweeping down from the north is tonic. It is heavy, and issuing from antiseptic altitudes, drives the humid, germ-nursing air from our city streets. If we had arranged a process of refreshment like this at vast expense we should have been intensely proud of it. As it is we are intensely annoyed at it and occasionally a few people are frozen to death. The Weather Bureau warnings and the coal clubs are reducing the loss in property and lives.

If you are sleeping out it is of great importance to know when the mercury is going to take one of these swoops, for sleeping cold means little real rest because one’s muscles are tense, and the next day’s packing needs all the relaxation one can get. Two generalizations govern pretty much every change of temperature: the mercury will rise before a storm and it will fall after one, winter and summer, but much more conspicuously in winter.

There are two reasons for this. Our cyclones usually cross our country over such a northern track that over most of the country the air drawn into them comes from the southern quarters and is therefore warmer than the air previously flowing from the anticyclone. Also the process of precipitation causes heat. This is true to such an extent on the coast of Ireland where it rains most of the time that a scientist has computed that the inhabitants get from one-third to one-half as much heat from the rainfall as they do directly from the sun. Thus a normal storm is doubly sure to warm up the environment.

In summer the reverse is partially true, for very often the rain does not begin until the actual center of depression has passed and the west winds have begun to exercise their cooling influence. So that in summer we have a sultry, sunny day as the first half of the storm area and then a cooling shower. Also after two or three days of warm weather in spring and autumn we have a rainstorm of the winter type which lowers the temperature instead of raising it. This is because the heat produced by the storm is less than that of the sun’s rays intercepted by the clouds. The clear skies of the preceding anticyclone had permitted the land to warm up very fast under the midsummer sun, and the clouds of the cyclone, by cutting off the supply, had made a relative chill.

In winter the sunrays are so much feebler because of their slant and radiation proceeds so rapidly under the dry air of the anticyclone that a much greater degree of cold is produced than when the cyclonic clouds prevent the radiation. Therefore the rainy area is the warmest of all. Even in summer the winds from the southeast, south, and southwest are warmer than those from the opposite quarters, not only because they blow from a quarter naturally warmer on account of the sun, but because they are surface winds and have absorbed some of the heat from the soil. Being denser, they absorb it more readily and hold it longer.

The change, then, from the period of fair weather to that of storm brings an increase of temperature. But the rate of increase varies. The faster the storm is approaching the faster the temperature will rise; and the route of the storm’s center makes all the difference as to the amount of the rise. If the wind shifts by way of the north and holds in the northeast until precipitation begins the rise in temperature will be very slight. The great snowstorms of the northern half of the country occur under just such a circumstance. If the wind shifts by way of the north but gets around to the east or even southeast before the precipitation starts the rise in temperature will be more pronounced, as much as thirty degrees sometimes in a few hours, and the winter storm that started in as snow soon changes to sleet and rain.

If the wind shifts by way of the south and then into the southeast the rise will be vigorous and the storm will likely be a comparatively warm rain. If the wind shifts only so far as the south the rise will be highest of all and blue sky will often appear between the showers, showing that the air is heated to a considerable height.

The progress of the temperature changes from the maximum of the cyclonic area to the minimum of the anticyclone is also dependent upon the wind. If the storm center is passing south and the wind begins to pull into the northeast and north the temperature will fall steadily and slowly. The rain or snow often cease gradually by the time the wind has reached the north, but the temperature continues to fall slowly until it reaches very low levels in mid-winter. If the storm center is passing north of you the wind which has brought most of the rain while it was in the southeast with comparatively high temperatures swings into the southwest, the temperature falls somewhat.

There is usually a final downpour and a rapid shift of the wind into the west or northwest, but almost never directly into the north. The temperature falls several degrees in a few minutes, quite unlike the gradual decline of the northeast-by-north shift, and clear skies come at once with rapidly diminishing temperatures. In the vicinity of Philadelphia a fall of twenty-five degrees would be most unusual on the northeast shift,—such storms reaching 38 degrees and falling to 15, while with the other shift a fall from 55 degrees to 15 would not be unusual. Of course any one set of figures given could only show the tendency and not the rule or limits.

After the manner of the wind-shift the intensity of the storm is a good gauge of the temperature change to be expected by the camper. As a rule the greater the intensity of the storm the greater will be the degree of cold that follows it. The storms that have a complete wind circulation about them are always more severe than those with incomplete circulation and are invariably followed up by some reduction in temperature. If the decrease is not proportionately great and the subsequent wind has only a moderate clearing quality look out for another cyclone.

In such a case the temperature is the best witness of the contemplated change. For instance, after a summer thunderstorm a decided coolness is de rigeur. If this does not occur it means nearly every time that there is another thunderstorm in process of construction. There may be not a cloud in the sky, there may be no wind (although there should be) so that the course of the thermometer is the only means of telling what is to be the next event. Anybody can take a thermometer with him although a barometer—the most accurate forecaster of all—may be thought too much expense and bother.

At some future date the Weather Bureau will be able to predict the temperature of seasons in advance. This, together with the amount of rain scheduled to fall, will be an invaluable aid to everybody and to the farmers most of all. At present mild seasons that have severe storms without the appropriate degree of cold after them cannot be entirely explained, let alone being prediscovered. They all hinge upon the more or less permanent areas of high and low air pressure over the oceans and international meteorological service has not progressed far enough to support many ocean stations as yet.

Sometimes clear weather may intensify, growing brighter, stiller, colder. This is because the pressure is increasing. Cold seasons are distinguished usually by a succession of anticyclones. There is no way of telling how long a certain spell of cold weather is to last, but I have noticed that the same characteristics rarely predominate for longer than a month at a time. In other words, if December has been warm and rainy, January will likely be cold and dry. Of course, that is precisely the unscientific sort of generalization which the Bureau very rightly frowns upon, but which one may nurse privately until science has provided a substitute as she already has in so many instances.

With a little practice it is an easy matter to estimate the temperature to within a very few degrees. Try guessing for a few mornings and then look at the thermometer. You will hit within three degrees every time after a week of this.

Allowance must be made for the amount of moisture in the air and for the force of the wind. Damp air feels colder by several degrees than crisp, dry air, and a breeze increases the difference still more. Air in motion is not necessarily colder than calm air. As a matter of fact the lowest temperatures of all are recorded about sunrise after a still, clear night. The amount of radiation accomplished during the last hours of the night is amazing, and the downward impetus of the thermometer is often carried on for an hour or more after the sun has appeared above the horizon. A self-recording thermometer is an amusing toy which will show this and becomes a valuable instrument if one raises fruit.

In winter three o’clock of an afternoon sees the highest temperature usually, and in summer this maximum occurs as late as half-past five, due to the fact that the sun can pour in its heat faster than the earth can radiate it off. For the half hour before and after sunset, particularly in winter, the loss of heat is relatively greatest; then the pace slackens till three or four in the morning, when the plunge of the mercury is accelerated until the rays of the rising sun counteract the radiation.

If the mercury does not rise appreciably on a clear winter’s day it is a sign that a cold wave is stealing in, due, doubtless, to a gradual increase in pressure without its customary bluster. Very often snow flurries predict its approach, but this may be so gradual that only the restriction of the daily thermal rise may indicate it. By the next morning the temperature will likely be twenty degrees colder.

If the mercury does not fall on a clear winter’s night it is a sign that a layer of moist air not far above the surface of the earth is checking the normal night radiation. Unsettled weather is almost sure to follow unless this wet blanket is itself dissipated and the mercury takes its customary tumble before morning.

If the temperature falls while the sky is still covered with clouds clearing, possibly after a little precipitation, will soon follow.

Hot waves approach insidiously. A night will not cool off as it properly should, the sun will rise coppery, and while the day is yet young everybody begins to realize that all is not exactly right. But the heat increases usually for several days, not only by reason of steadily lowering pressure, but also by accumulation. Finally when a climax is reached it departs abruptly on the toe of a thunderstorm.

A cold wave reverses the process. It arrives abruptly on the heels of a departing cyclone and, after losing power, steals away without any commotion whatever. Its rate of progress is in close relation to the cyclone ahead of it.

Our mountains play a great part in our weather. They are a right arm of Providence to our agricultural communities. Due to their north and south trend a cold wave of any severity reaches the Pacific Coast only once a generation. Just once has snow been observed to fall at San Diego and it is so rare south of San Francisco that many people never have seen a flake. East of the mountains the belt of desert makes natural crops impossible for a thousand miles, but if they crossed the continent all the territory north of them would have such a cold climate that none of the present enormous crops of Canada and our northern states could possibly be grown. It is also due to the wide insweep of winds from the Gulf that the plains states are so well watered.

CUMULUS

Courtesy of Richard F. Warren

The tops of cumulus are irregular, looking like wool-packs; the bases are flat. The true cumulus shows a sharp outline all the way round. Its shape is in constant change due to the strong winds it is encountering. It is caused by the swift uprush of warm air on a sunny day. This cloud is a sign of fair weather, because the base is not large, compact, or dark enough to threaten rain and its comrades are also disjointed. If the cumulus grow darker toward the horizon and increase toward evening a squall is likely.

In lesser fashion the Appalachians protect the Atlantic seaboard. They withstand the impact of the cold waves to a great extent, although they are not high enough to divert the flow of cold air entirely toward the south and it is not desirable that they should. As things are the cold strikes Alabama before it hits New Jersey, and is often more severe there.

Comparative cold is often registered by the green color of the sky. A fiery red continues the prevailing heat.

The day that is ushered in by a fog, in summer, will likely be warm, providing the fog lifts by ten o’clock.

The temperature of a night with even a thin covering of clouds will be a good deal higher than if the sky is clear. In the British Isles the whole difference between freezing and no freezing lies with the fairness of the heavens. Everywhere frost will not form while the sky is covered, although the temperature may be below the freezing point. In summer radiation on a still clear night may be so rapid that frost may follow a temperature of fifty degrees at nightfall.

The temperature at the surface of the earth may easily deceive, as a colder or warmer stratum of air may overlie that immediately next to the ground. I have seen water particles fall when the temperature was as low as 16 degrees above zero, showing that the stratum of cold air was very thin. Our sleet storms in which immense damage is done to trees and telegraph wires occurs from just such a situation,—a cold, shallow layer of air close to the earth, with the warm moisture-bearing air flowing over it. The reverse of this situation is not uncommon—the sight of a snowstorm proceeding merrily along with the ground temperature at 35 or even 40 degrees.

Coming warmth may be noticed by the increase in size of snow flakes, with finally hail and rain. Coming cold is foreshadowed by hail mixed with the rain and lastly snow flakes which have a tendency to decrease in size. Colors of the clouds predict temperature changes, but it takes much practice to distinguish the cold, hard grays from the soft, warm ones. A warm sky is always less uniform in color than a cold one. The colors of winter sunsets are, as a rule, much brighter than those of summer skies.

The stars seem brighter on a night that is to be cold. If they twinkle it is because of rushing air currents, and if the wind is from the northwest the result may be a subsequent lowering of temperatures.

The whole question of whether it will be colder and how much is vital to the camper and if the signs of change are taken along with the look of the clouds and the direction of the wind he need never be wrong as to the direction the mercury is going, and will soon be able to guess the distance pretty fairly.

RAIN AND SNOW

East of the Mississippi River rain falls with the utmost impartiality upon every locality. Thirty to fifty inches are delivered at intervals of three or four days throughout the year. And if there is a slight irregularity in delivery one can be sure that from 125 to 150 of the 365 days will be rainy. Occasionally there is a more or less serious hold up of supplies, but this rarely happens in the spring of the year and never happens to all sections at once. And if there is a desire to make amends for the drought, we have what we call a flood and blame it on the weather instead of on our precipitous denudation of the watersheds.

West of the Mississippi particular people have to go to particular places for their rain. If they like a lot of it they must go to the coast districts of Washington or Oregon where they can have it almost every day. It rains a good deal at Eastport, Maine,—about 45 inches a year; that is, nearly an inch a week,—but at Neal Bay, Washington, at about the same latitude, in one year it rained 140 inches, and it never stops short of 100 inches any year.

On the other hand, if the Washington people are tired of it they need only escape to Arizona where it rains about two inches a year, and they can live in an enterprising hotel down there whose manager believes that it pays to advertise the sun. He guarantees to provide free board on every day that the sun doesn’t shine.

In the plateau section enough snow falls every year to store up enough water for irrigation purposes, and the little rain that falls arrives in just the right season to do the most good, the spring. In California what the farmers lose in amount they make up in the regularity of its arrival.

North of the Ohio River most of the precipitation from November to April is snow. About 50 inches of it falls on the average over this tremendous territory. And it is more useful than rain,—the handy blanket that makes lumber-hauling easy, that keeps the ground from freezing to Arctic depths, that fertilizes the soil, and that acts as a great reservoir, holding over the meat and drink of the vegetable kingdom till the thirsty time arrives. In upper Michigan and Maine the average depth becomes 100 inches. Averages are very misleading when snowfall is being considered, some winters producing very scanty amounts and others heaping it on to the depth of 185 inches once at North Volney, New York.

South of the Ohio the depth varies from substantial amounts in some winters to almost nothing in others. Snow has been observed, however, in every part of our country except the extreme southern tip of Florida. Once and only once on the records a great three-day snowstorm visited all of southern California, extending to the Mexican border and to the coast.

The strip of country between the parallels of New York City and Richmond comprises the section wherein each winter storm is one large guess as to whether the precipitation is to be snow or rain. A compromise is usually affected in this way. Before the clouding up began the mercury may have stood at ten degrees below zero. As soon as the wind acquired an easterly slant the temperature increased. As it neared the freezing point the snow would begin, first in flakes of medium size which would enlarge until after a particularly heavy fall of a few minutes they would at once almost cease. Hail soon would succeed, the mercury still rising, and often the hail would have turned to rain before the freezing point of the air of the immediate surface of the earth had been reached, turning the snow already on the ground to slush and making a holiday for germs.

One can always tell when this change to warmer is about to occur because the clouds which have been part and parcel with the obscuring snow suddenly show, not lighter but darker. The sudden increase in size of the flakes is another infallible symptom of increasing warmth in the atmosphere for each large flake is a compound of many smaller ones. When the temperature is low the flakes are very small, being grains and spicules in the severe blizzards of the west and falling as snow-dust in the Arctic. In the heavy storms of the guessing-belt the flakes are not necessarily small.

I have noticed (in the latitude of Philadelphia) that our largest storms begin very leisurely indeed with small and regular-sized flakes. A quarter of an inch may not fall in the first hour. As the center nears the snow comes ever faster and larger, but not large, flakes are mixed with the original-sized flakes. Snow dust is apparent. At the height of the storm flakes of all sizes except the very large are falling, denoting great activity in the strata of air within the storm influence. In the ordinary storm an accumulation at the rate of an inch an hour denotes a storm of considerable intensity.

The snow will likely keep on falling as long as the flakes are irregular in size. If they grow large and few or very small a cessation is likely, even though the wind is still blowing from an easterly quarter. The amount of snow likely to fall can be gauged not only by the process of flake-change but by the rate at which the wind rises. A storm’s intensity is measured by the amount of wind. A storm can be a storm without a drop of rain or flake of snow if only there be enough wind. And as long as the wind in a snowstorm keeps rising the storm is likely to go on, probably increasing in volume of precipitation.

If the wind shows a tendency to edge around to the southeast there is danger of the snow turning to rain; if the wind veers slowly to the northeast the temperature will fall slowly and the rate of precipitation will likely increase for a while. In such instances the snow does not continue to fall after the wind has swung west of north. Often clearing takes place with the wind still in the north or even a point east of north.

Contrary to superstition snow may begin to fall at any hour of the day or night. But certain hours seem more propitious than others, owing no doubt to the tendency of cooling air to condense. Three o’clock of an afternoon and eight o’clock in the morning are favorite times, the one being the hour of a winter afternoon when cooling is begun, the other the hour when the coldest time is reached and condensation likely if at all. Of course, one remembers storms beginning at nine, ten, eleven, and every other hour.

Storms that begin in the morning seldom reach much activity before three o’clock in the afternoon, while those that begin then quickly increase in intensity as evening draws near and the sun’s warmth is withdrawn from the upper air-strata. More snow falls at night than in the daytime, also. Snow is more delicate than rain and perhaps more responsive than rain to the subtle changes of the atmosphere. Possibly there is no ground on the Bureau records for these ideas, possibly storms have a tendency to start from the Gulf on their northeastward journey and so reach Philadelphia oftener at one time than another. I would like my notions confirmed that snowstorms increase at nightfall, and that they prefer to start operations at sunrise and about sunset.

For the camper the snowstorm need have no terrors. It gives a long warning of its approach. It comes mostly without destructive winds. Its upholstery protects and warms the walls of one’s tent. It adds beauty to the leafless woods, interest to the trailer, and a hundred amusements among the hills.

But the value of snowy weather is not only measured by its beauties and commercial uses. There is another way: make it read character for you. Watch the reactions toward the first snowfall of half a dozen kinds of people. It will show you what they are; give you a very fair measure of their youth.

Our atmosphere contains a lot of moisture that never gets precipitated. You can prove this on any warm day by noticing the way the atmosphere acts toward a glass of ice-water. When the air of the room is much warmer than the surface of the glass it surrenders its moisture willy nilly. Sometimes this condensation is enough to cause a miniature rainstorm that trickles down the outside of the tumbler. If a small cold surface can wring so much water out of a little air it is small wonder that we get an inch or so of rain from vast currents of air at unequal temperatures.

Try to visualize the process. A stream of vapor has been warmed and is ascending. A mile up and it has cooled not only by the reason of altitude but also by the process itself. About each little dust-particle in the surrounding area vapor forms—vapor cannot form without something to form on, there being always enough dust from deserts and volcanoes to go round. If the cooling proceeds the tiny globules enlarge and as they increase in weight they settle and fall. Falling, they unite with others.

If the air-strata are very warm and thick the drops may grow to a very considerable size. We see these in the middle of our great winter rains when the insweep of southern winds with all their warmth and moisture is very extensive. Also the first few drops that come from the thick, hot lips of the thundercloud are usually immense.

The best way to measure the size of a raindrop is to have it fall in a box of dry sand. It rolls up the sand and measurements can be easily and accurately made. But the most interesting way is to let the first drops of the thunderstorm fall upon a sheet of blotting paper. If the same sort of blotting paper is used the measurements will be of just as much importance for comparison. Circles as big as teacups are formed sometimes.

Heavy drops in winter mean a heavy fall, because they denote high temperatures which are uncommon and are bound to be followed by considerable condensation as the cooling proceeds back to normal temperatures. Small drops in summer mean either cooler weather, or sudden condensation. Small drops in winter are a sign of very thin moisture-bearing strata, or low temperatures, indicating that the rain will be light, protracted, and liable to change to snow.

Hail is frozen rain. Winter hail is small and harmless and rarely falls to any depth because the exact temperatures that bring forth the hail rarely continue for very long at a time. Hail in winter is merely the stepping stone to either rain or snow. But in summer hail is a serious matter. It shows that there is a violent disturbance of the atmosphere in progress. Vertical air currents, probably abetted by electricity,—the authorities are not sure—often carry the stones up several times. They take on layer after layer, coalesce, and sometimes fall the size of eggs, apples, or any other fruit, barring melons. The usual summer hail does not exceed the size of a robin’s egg. Even a projectile of that size, however, falling for a half mile or more has a tremendous destructive power. Greenhouses suffer, birds are killed, cattle stunned, and loss of life has been known to follow. In August in 1851 in New Hampshire hailstones fell to the weight of 18 ounces, diameter 4 inches, circumference 12 inches. In Pittsburgh stones weighing a full pound have crashed down, and in Europe where many destructive storms have occurred there are official records of even greater phenomena. The lightning accompanying these hailstones is usually very severe. A flake or ball of snow forms the nucleus of a hailstone.

If a thundercloud looks particularly black or if it can be seen in commotion think of hail and seek shelter. It is pretty difficult to predict exactly when hail is going to fall in summer. It is a possibility with every large storm, but a probability with only a very few during the summer. It accompanies tornadoes.

In winter hail falls before a rainstorm, even when the ground temperature precludes the possibility of snow; some lingering stratum of cold air has ensnared the drops on their way down.

Snow is not frozen rain. It has an origin of its own. It is born in a temperature consistently below freezing and on the condensation of the invisible moisture becomes visible as a tiny crystal. These infinitesimal crystals unite and form larger, hexagonal shapes, elongated or starry. They are wafted along, sinking, all slightly differing one from another, although forming a few types. These types have been photographed and catalogued and very often the altitude from which the snow is coming may be learned from their shape and design. But this branch of science is young yet and confusing and the outdoor man has surer signs of the vicissitudes of the storm, in the general size of the flakes, the power and direction of the wind, the clouds and temperature. The possibilities of flake-study as a means of forecasting are many and of value as is anything that tends to unveil the secrets of the greater heights.

Snowflakes are so light that after the storm processes are over and the sun has come out the residue may still float lazily to the ground.

The wild disorder of the snow flurry will only last a few minutes and never leave much snow on the ground.

Snowstorms that come on the wings of the west wind may be severe, but they will be short. They are unusual in the east, but sometimes the heaviest snows of the western states come on the sudden cooling that follows the shift to west.

Snowstorms arriving on a high wind last only a few hours.

Snowstorms that are long in gathering and increase to considerable intensity continue a long while.