Chapter IV: Sky Signs for Campers (1)

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.

_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.

_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.