Reading the Weather Part 3
Montgomery, Alabama, "During March, April, and May fruit and early vegetables are subject to damage by frost."
THE THUNDERSTORM EXPOSED.
Probably nothing in the world causes more terror than a flash of lightning. In an able-bodied thunderstorm playing about a city there are several dozen flashes, and every one of them brings trepidation, fright, or positive terror to thousands of human beings,--oftenest women, sometimes men, and occasionally children. Yet probably there is no alarm in the world so ill-founded.
Thunderstorms play pretty generally over our three million square miles with their hundred million population. Yet lightning picks out of this crowd only three hundred people a year who are foolish enough to be killed. That is, only three persons in each million to be sacrificed to the most astounding and beautiful display in the world, a mere handful compared to the mounds of motor car victims or to the 33,068 deaths a year attributable to railroads and the perils of track-walking.
The trouble about the thunderstorm is that it does not lull one into the sense of insecure repose. It is too obviously after one. If the thunder were toned down a bit and the lightning a trifle duller the alliance might claim its thousands, like the inconspicuous housefly, and never meet an objection. But until the thunderstorm foregoes its bravado it will continue to bully the ladies into hysterics.
Of course, there is always the sporting chance that you are one of the three in your particular million to perish.
But you can lessen the chance. You must not seek refuge under a tree. You should not take doubtful shelter in a barn. And you had best not sit in a draft by an open window if there is a tree just outside it. By these three avenues most of the thoughtless three hundred (a year) invite their end.
Trees that are tall and otherwise exposed are struck oftenest. The electricity in the cloud and the electricity in the earth are always endeavoring to combine. When this tendency becomes so strong that the resistance of the intervening air is counteracted the electric discharge between thundercloud and earth takes place. This happens most frequently from some pointed thing as a steeple, a tree if they are good conductors. Men and animals are sometimes charged with the electricity opposite to that of the cloud. When the lightning is discharged, even at a distance, the bodies revert rapidly from the electric to the natural state. This return shock or concussion occasionally proves fatal.
That is the reason that trees are such poor protectors from the storm's fury. Better a wet skin in the middle of a field than precarious dryness under an oak or cherry or tall pine or almost any other tree. If it should hail hard enough to stove in your head take to a beech or a small spruce.
Barns are struck so often because the body of warm, dry air in them favors the pa.s.sage of electricity. Those who hide in barns are sometimes cremated. After a severe thunderstorm in the Poconos I have seen as many as three barns on fire at once.
Open windows, porches, and exposure generally are safe, but not safest. The cellar, that old stamping ground, is where instinct takes a few. Any closed room on the side of a house away from trees is good enough. But the risk of annihilation is so very small that one is repaid for taking it by the spectacle. A great thunderstorm surpa.s.ses anything in nature in the matter of architecture, coloring, directness, and surprise,--which, with selection, comprise the essentials of art. Imagine the crowds that would pay to wonder at the sight if a thunderstorm could be staged, say, at the Hippodrome!
Some hot morning, if you have time to watch, you may see a thunderstorm born in the mountains. The warm, moist air flows up the mountainside and the essential start is made. Cooling, this air first shows as a fluffy cloud that soon grows harder in appearance and becomes tufted at the top. Its little belly swells and grows blacker. It hovers over the valley. Others add to it. Suddenly a sort of adolescent thunder is heard. The tension has become too great. A definite consolidation is visible, a fringe lowers, and a few drops of rain may reach you.
The incipient storm moves off, and having started a whirl within itself, increases, like a rumor, as it goes. Before it has moved beyond your horizon it may have become a large patch of dark blue with billowy white crests on the top, and underneath hangs a curtain of rain. Chances are that it will not go far before encountering conditions that dispel it, but it may cover half a dozen counties before nightfall. As a rule these little heat thunderstorms do not amount to a great deal. They are originated by local conditions and leave things pretty much as they found them.
But when a cyclone is pa.s.sing in summer a series of thunderstorms or heavy showers with some thunder frequently take place instead of the all day winter rain. These thunderstorms mount up against the wind. Their clouds are black. The word black is an indulgence of the human weatherman meaning, of course, any dark color,--a black sky would terrify the most hardened of meteorologists.
The cyclone winds come from the south or southeast just as they do in winter, but this quarter may not bring the heaviest rainfall in summer. There may be showers or even clear skies, but the day will be humid and hot. A haze of cirro-stratus cloud will gradually overspread the sky from the west, darkening into a blue from the original whitish or gray. Lightning does not appear from the cirrus, but after the sky has grown pretty dark a ridge or tumbled cloud will be seen low on the western horizon. Meanwhile the wind will have died down.
The lightning, at first only a faint glimmer, will have become more frequent and noticeable. If it is striking at a distance of fifteen miles the thunder will not be heard. As soon as the storm center, where the heaviest rain and the electrical display are taking place, gets within the fifteen-mile radius thunder will be heard to growl, and the tumbled c.u.mulus clouds which may have lain along the horizon for hours will begin to approach. The storm will be upon you in ten minutes likely after the arc of foreboding blue and white cottony cloud has begun its charge across the sky. Light quickly fades from the heavens. The wind drops entirely. Streaks of lightning burn downward.
Behind the arc stretches a curtain of uniform blue or gray. If the gray is lighter in places the rainfall will not be heavy. If the curtain is a uniform blue a heavy rain is sure. If the bow of clouds can be seen to tumble or is continuous and approaches fast the wind is certain to be severe,--may be from 30 to 60 miles an hour for the first few minutes. Sometimes a cloud of dust advancing before it demonstrates its force.
This moment immediately before the storm breaks is the dramatic moment of the entire cyclone. As in a tragedy, the interest has built up to this supreme occasion, this knife thrust, from which interest recedes until clear skies show that the play is over. From 12 to 36 hours is the usual time required in winter. In summer the cyclone takes even longer to pa.s.s a given point, but the period of rainfall, in which the winter storm's amount is often surpa.s.sed, may not last fifteen minutes. First the blow, then a crash of thunder, and the rain in big drops, which lessen rapidly in size as the whole world seems involved in the vast forces of the storm center. Most of the precipitation occurs in the first fifteen minutes, sometimes in the first five. A hearty storm will deliver an inch in short order. Although the rain continues often for an hour and sometimes in the storms that are attached to a well-defined cyclonic system there will be two or three robust thunderstorms in succession, yet the first downpour is usually the torrential one and the others die away until the conditions that caused the outbreak have pa.s.sed off. With the severer storms hail falls.
The general condition of the air after a thunderstorm is cooler, dryer, and more invigorating than before. Ozone has been liberated, dust has been washed from the air and vegetation. The surest sign of a continuation of unsettled weather is the failure of the atmosphere to cool off. If the air remains sultry and heavy and depressing another shower is due. In such circ.u.mstances the wind will not have begun to blow with any great promise from the west.
A close, sultry morning is the best indication of a thunder-gust. The large piles of c.u.mulus clouds are called thunderheads for the very reason that they almost always precede a thunderstorm. The heaviest electrical disturbances have cirrus clouds a few hours in advance of them very much as their winter relatives. A thunderstorm that does not cause the barometer to fall considerably will not amount to a great deal.
At night the different kinds of lightning furnish a running commentary to the storm. On calm evenings the sky will be cloudless, with perhaps the exception of a low rim on the northern horizon. Yet flashes of lightning, of course without thunder, may be seen illuminating that entire quadrant of the sky. This is called heat lightning and is popularly supposed to be the result of the heat only. As a matter of fact it is caused by a normal thunderstorm that is operating below the horizon. Reflections from this storm are shown on the rim of clouds, or if no clouds are visible, on the bowl of the sky. If you see lightning be sure that there is a storm somewhere.
If this disembodied sort of lightning continues to flash from the western sky it is quite possible that the storm will reach you. If it shows on the northwest or north of you the chances are that the storm will be carried around. If the wind is from the southwest and the lightning appears there only the progress of the clouds will show whether the storm is pursuing the normal track from the west and around you or whether it is edging up toward you. One cannot be very well surprised by a thunderstorm of any energy in camp as the lightning shows as much as two hours before the storm breaks and the thunder gives fifteen minutes' notice on most occasions.
The sort of lightning that spends itself illuminating the clouds in serpents and willowy branches confines itself to the alt.i.tudes and is very beautiful and harmless. It is accompanied by thunder that sounds hollow, that rumbles over the sky, and usually does not end with the crash and thud of the more vigorous variety. Such lightning and such thunder are more often connected with the sort of storm that comes up very swiftly on a western wind. It gives shorter warning than any other sort of thunderstorm and is not connected with the cyclonic area. I have known such a storm to manifest itself low in the west, approach, and break within twenty minutes. Much wind results and not much rain, although the temperature falls. Lightning with storms of this impromptu kind rarely does any damage.
But if the storm rises slowly against the wind, requiring an hour or two or three to approach and break, the lightning will grow almost continuously, some of the flashes being broad streamers cleaving the western sky. It is this sort of lightning that does the damage. The thunder, instead of rolling like an empty barrel, hits into a series of concussions. If the lightning strikes an object nearby the crash is rather appalling. There are several freak sorts of lightning such as the ball form, which are rare.
The approach of the center of disturbance may be gauged by the length of time that elapses between flash and crash. In reality the thunder occurs immediately after the discharge of electricity, but sound travels so slowly, compared to light, that a minute may intervene between stroke and clap. You may count the seconds, noticing the regular decrease, signifying the nearing of the crisis. Soon a flash in front and a simultaneous peal will show you that you are in the thick of things. The next bolt or two may hit very close and you can appreciate what it means to be on the firing line. Then the next river of fire with its detonation streams behind you and you are saved.
In a severe thunderstorm there are several centers, several nuclei that shed destruction like great batteries and their progress over and beyond you has its thrills. You may find the exact number of feet away that the bolt hit by multiplying the number of seconds elapsing between the lightning and thunder by 1120. But an easier way is to allow a mile for every five seconds on the watch. One or two seconds, and you are pretty near the center of the fray.
Lightning compresses the air, leaving a partial vacuum. The other air rushing in to fill this partial vacuum forms the wave motion that produces the noise. That is the whole why of thunder. The reason thunder rolls is that the lightning is a series of discharges each of which gives rise to a particular detonation. If lightning were but one discharge, the thunder would be but one stupefying crash. Reflections from the clouds and from layers of air of different densities and from the ground are agencies that prolong the sound.
Our atmosphere is never lacking in electricity. This electricity is always positive in clear weather and sometimes negative in cloudy. Science concludes, then, that negative electricity invariably indicates rain, hail, or snow within a radius of forty miles.
Moist air is a good conductor. Our powerful motors can now produce a spark of electricity several feet long. But some of the flashes that shoot across the sky in a big storm extend over five miles. The duration of the flash varies from 1-300th of a second to a second. The reason that lightning does not always pa.s.s imperially along a straight line is that some air, either moister or warmer than the air around it, offers less resistance. The lightning takes this line of least resistance along the pathway of warmer or less dense air.
Alt.i.tudes of thunderclouds vary. They may hover above the earth at 800 feet. They may be a mile high. They have been observed on peaks of mountains three miles high. Many other electrical phenomena are observed in the mountains. The study of these will undoubtedly benefit meteorology and perhaps go far to explain the unsolved problems of the Service.
One kind of thunderstorm that is rather rare is that which arrives in winter with the pa.s.sage of an energetic cyclone. Often when the wind, having been in the southeast for most of the storm, is pa.s.sing around and reaches the south or southwest the rainfall culminates in a deluge and thunder is heard. One or two such storms are a winter's complement. They usually terminate the rainfall for that particular cyclone. I have never heard of damage caused by these winter electrical storms, and they occur only in exceptionally well-developed areas of low pressure.
Lightning has many times been observed during heavy snow storms. I have never heard any thunder with it. The discharge must have been very faint.
[Ill.u.s.tration: STRATUS.
Courtesy of Richard F. Warren.
Stratus is merely lifted fog in a horizontal form, the lowest of all, and the simplest as regards structure. It means neither rain nor snow and the apparent clearness of the blue above it would indicate clear weather to come. But through the break in the stratus near the horizon shows a cloud of firmer texture, which is less rea.s.suring. Stratus over the land in winter takes the appearance of long bolsters of gray through which a pale blue sky shines. Such clouds may blanket the sky for days without causing a drop of rain. If they show a tendency to glaze over expect snow or rain, but not in large quant.i.ties.]
The fascination that a thunderstorm has for many people is explained partially by the fact that one sees the whole process from beginning to end. The officials of the Weather Bureau have this privilege as regards cyclones. It is their business and pleasure to watch the setting up of these vast storms, to follow them on their journey. It is small wonder then that they find the spectacle fascinating.
THE TORNADO.
The birds, the flowers, and the tornadoes are all busiest in spring. And the tornadoes probably make the largest impression.
A tornado is merely a whirl of air, caused, as are all the other whirls, by a striking difference in temperature in adjacent areas. A tornado is a local and restricted example of the same thing that a cyclone is. But a tornado rarely crosses more than a single state; a cyclone strides continents. A tornado lasts, in one place, about a minute; a cyclone affects the weather for three days. A tornado never survives the night; a cyclone plods on for a week. And yet if you are betting on destruction put your money on the tornado. What it lacks in the realms of s.p.a.ce and time it makes up in intensity. Its sting is fatal.
Tornadoes occur chiefly in the spring because the temperature changes are greatest then and it is from these that the tornado sucks its nourishment. Over the plains, for example, a limited area is abnormally heated by a local cause. Abnormal cold comes in contact with the abnormal heat. The great difference in pressure results in a spiral as it did in the cyclone, only in a very small spiral, and once begun its energy is self-aggravating. The whole thing moves off toward the northeast attended by the black cloud of its condensation. From the black cloud a funnel like an elephant's trunk sways back and forth, now touching the ground and now escaping it. The black cloud has been in the southwest for some time probably before it has commenced to move. The day has been very oppressive. The sun rose rather coppery, in all likelihood. As the black cloud with the swaying funnel nears a roaring is heard. Darkness falls. The roar increases.... Instantly it is over.
Now that you've been through a tornado you know how it feels,--almost. After the funnel pa.s.ses hail falls, lightning flashes through the lessening murk. Heavy rain succeeds, and if you're alive you go out and rescue the perishing.
The wind velocity in the path of a tornado is enormous,--anything up to 500 miles an hour,--but no instruments have been devised to withstand the strain. Varying pressures are responsible for the destruction. As the funnel pa.s.ses over a house where the normal air pressure is about 2,000 pounds to the square foot it removes 1,500 pounds for an instant. Naturally the outside walls cannot withstand this enormous inside out pressure and the house explodes like a projectile. Only under such conditions could the vagaries of matter,--straws piercing logs and chickens bereft of every feather--be perhaps not explained but pardoned.
Stories of any degree of incredibility crop up after each tornado, often with accompanying photographs as proof. People are plastered with mud, pianos are deposited in neighboring lots, babies are hung up unhurt by their clothes in tree-tops, and often one person is killed and another nearby escapes unhurt, Bible-fashion.
Tornadoes may form almost anywhere, but they are never found on the immediate Pacific coast. They are most common in the Mississippi Valley, are rather common in the Gulf States, and have occurred throughout most of the East at one time or another.
Since there is no way of stopping them the next best thing is to know the conditions that make for their formation. If the Weather Bureau predicts a cold wave for sections of the country where the weather is already abnormally warm the line of meeting will probably produce a tornado somewhere. The officials, however, advise you not to worry until you see the intensely black cloud in the southwest trailing its funnel. See where this funnel is tending and run the other way. All tornadoes progress from the southwest to the northeast. Bad as they are, this makes them far less terrifying than if they whipped back and forth over a town or chased you around the pasture. If you happen to be in the house, take to the cellar, the southwest corner of it. If you can't escape lie face down to the ground.
The only tornado that I have ever witnessed was an undeveloped one in England, and a bit lethargic compared to those of the Prairie States. But even this blew an entire train off the track. It had all the other appurtenances of a tornado, the hail, the twisted trees, the narrow southwest to northeast path. The fact that the houses had only corners of their roofs blown off showed that as a tornado it was distinctly second-grade and without power to explode.
England, shortly after, was raided by three water-spouts. These phenomena are caused by precisely the same conditions as are the tornadoes. They form over the sea, and the funnel is composed of water. They take considerable bodies of water up into the skies and torrential rains result over adjacent districts. If I remember correctly, two of the English water-spouts broke against the cliffs and the other, moving inland in modified form, gave Gloucester a nine-inch rain. Ships have been known to fire cannon at these spouts. If one hit a boat directly damage might be caused, but they have little of the destructive force of the tornado.
As our country builds up the destruction from this most powerful of all phenomena is likely to increase. Bureau warnings over phones may result in the saving of some lives; cellars will undoubtedly be built in the princ.i.p.al zones. But the problem is an interesting one, for unlike the waterspout, cannon cannot be employed to shatter an emptiness that stalks the more malignantly the emptier it is.
THE HURRICANE.
The tropical hurricane is undoubtedly nature's mightiest exhibit. The hurricane is the cyclone par excellence. It does not differ from our ordinary weekly cyclone in the essentials of wind rotation or pressures or rainfall; but it does differ in place of birth, in its course, and chiefly in its intensity.
The genuine hurricane is a West Indian production. It is generally cradled in those islands south and east of Jamaica and Cuba. It is nursed by the trade-winds. The first notice of its birth is an alteration in these winds, which are among the most regular observances on our planet. An extensive formation of cirrus clouds spreads over the sky and the barometer, which has been stationary for some days, edges off and begins a long and gradual fall. Great rollers are noticed for a day or two before the winds rise. A hurricane moves slowly.
This tropical organization is superior in depth to our shallow, disc-like, continental cyclone which is one and rarely over two miles thick. The hurricane rears its head three, four, and even five miles high. Instead, too, of dissipating its force over thousands of miles at once it is only a few hundred miles in diameter. Its center moves methodically along at the not very impressive speed of fifteen miles an hour, while our cyclones hurry along at thirty. But the hurricane is thorough. The wind about its center reaches a velocity of 120 miles an hour. This velocity has never yet been attained on the surface of the earth by our trans-continental cyclone.
Our cyclone always has an eastward trend; the hurricane has a parabolic course. It begins by moving west on the trades, drifting and dealing destruction to the banana and sugar plantations of Jamaica. It enters the Gulf of Mexico, and since it is then pretty much out of the influence of the trades it curves to the right and begins to act like any other storm by heading directly for the St. Lawrence. If it pa.s.ses out through the Florida straits it never reaches the St. Lawrence but speeds up the coast and out to sea, usually at Hatteras to follow the shipping routes across the North Atlantic.
But if it has become so involved in the Gulf of Mexico that it cannot escape to sea again, it comes up through the Gulf States and on toward New England. Fortunately as it goes inland its intensity diminishes because it has not so much energy-giving moisture to draw from. Also its sphere of action widens, its embrace is less mighty, its characteristics more those of an ordinary continental cyclone. It manages, however, to deliver gales of 80 miles an hour along the coastal plain, increasing to 100 at the exposed places such as Hatteras and Block Island.
The intensest hours of a hurricane are those when its course is changing from westward to eastward. Enormous rainfalls accompany these storms, amounting to six inches in some instances. Since one inch of rain amounts to 100 tons per acre, and 64,000 tons to a square mile one can imagine the great amount of evaporation that has taken place to so saturate the air as to drench vast territories to such an extent.
While scarcely a year goes by without one of these West Indian hurricanes distinguishing itself on our sh.o.r.es the one that visited Galveston in 1904 eclipsed all. It chose to turn in the vicinity of the city. The gale increased to over 100 miles an hour and the wind gauge then blew away. The waters of the Bay were heaped up and three thousand lives were lost in the flood and wreck of flying houses. This peculiar storm did not turn northeast at once but ascended the Mississippi, turning at the Lakes and proceeding down the St. Lawrence after having spent a week in our country.
The listless doldrums have sent us 121 of these storms in the last generation. June has seen 8, July 5, August 28, September 40, and October 40.
Sea-yarners have seized upon the hurricane to energize many a flagging chapter, and particularly have they emphasized the eye of the storm. The eye is that vortex where contending winds neutralize each other into a calm, where the sun shines out through the scud, where the waves, relieved of the great pressure, leap upward in wild disorder. Then the center pa.s.ses and the wind flings itself upon the unlucky bark from the opposite quarter. Its first onslaught is always represented as being the fiercest of the whole storm and gradually lessening as the center drives farther away. This is true in the same way that the first attack of the thunderstorm is usually the fiercest, both being when the pressure begins to rise. This savage change to the northwest is naturally the hardest of all for the ships to bear as they must steady at once against the severest blast instead of gradually bracing for its culmination. In no department of meteorology has fiction adhered so closely to the facts as in the sea-rover accounts of the hurricane.
But in real life there is very little excuse for the vessel to be caught anywhere near the disastrous center of the storm. Indeed, for generations sea-captains have known how to escape the deadly eye. By watching the barometer and noticing in which direction the wind is working round they can tell the course to a nicety and estimate its speed. Then the wise ones run the other way for even the Olympics and Imperators of the sea are cowed by the might of the West Indian.
The typhoons of the West Pacific are similar manifestations.
The hurricane moves off from its birthplace so slowly that our Weather Bureau has an opportunity to size it up, to chart its probable course, and to warn shipping interests. The ship-owners, as a cla.s.s, appreciate the service of the Bureau and obey its warnings. Vessels with cargoes of a total value of $30,000,000 were known to have been detained in port on the Atlantic coast by the Bureau's warnings of a single hurricane. Now that a much vaster commerce will steam through these dangerous waters toward the Panama Ca.n.a.l the warnings will a.s.sume an even greater importance.
The best description of a hurricane that it has been my fortune to read is in a story ent.i.tled "Chita," one of the remarkable fictions of Lafcadio Hearn. As truthfully as a scientist and with great beauty of style he has pictured the long days of burning sun, the foreboding calm, the thickening haze, the ominous increasing swell of the ocean, a breathless night with the lightning glowing from between piling towers of cloud, the startling suddenness of the wind's attack, its fury, the hissing rain, the shrill crescendo of the gale.
CLOUDBURST.
It is the American tendency to exaggerate. We call every snowstorm a blizzard, every breeze a gale, every shower a cloudburst. In our generous vocabulary it never rains but it pours. Consequently if we, in the East, ever had a real blizzard or a real cloudburst we should be at a considerable loss to find words for an unprofane description. I do not know how they manage out West where these things occur.
A genuine cloudburst must be an amazing spectacle. It is caused by a furious updraft of wind keeping a rainstorm in suspense until so much water has acc.u.mulated that it has to let go all at once and the acc.u.mulation descends like a wet blanket.
This phenomenon is staged in the mountains; most often in the Rockies where melting snow and desert-hot ravines provide the necessary extremes of temperature. Wind blowing up a mountain-side can maintain considerable force,--so much that a man cannot possibly walk against it. Black thunder clouds brew on the peaks. Suddenly the collapse, and the person who tells the story afterward finds himself struggling in a torrent that a minute before had been a dry gulch. The moral of the story seems to be that if you are camping in the mountains and there is a strong upstream wind blowing and the clouds darken about the hill-tops and the thunder mumbles then don't make your bed in the creek-bottom lands. The high water marks of former freshets, but not of cloudbursts, show on the side of the stream.
Even in the less impulsive East a couple of inches of rain make a surprising rise in a little creek.
THE HALO.
The halo is a luminous circle around the moon or the sun. It is caused by the refraction of light pa.s.sing through moisture, which at the usual height is in the form of ice-crystals. The halo when complete consists of two large circles whose diameters are constant, 45 and 92 degrees. Then there are often other arches in contact. At each point of contact occurs a parhelion which is a mock sun of brilliant colors and called a sun-dog. Since the sun-dog is brighter than the other parts of the halo it sometimes appears when the rest of the halo cannot be seen. Sun-dogs hunt in pairs or fours. If the halo is colored the red is on the inside. When the colors are caused by diffraction instead of refraction, the red is on the outside of the prismatic ring and the halo is called a corona.
Having now satisfied the demands of science all that can be forgotten except that the halo around either sun or moon means excess moisture in the atmosphere. The wide halos are seen in the high cirrus clouds 25, 36, 48 hours in advance of a cyclone. At first the ring is very wide and faint with several stars in it. If the storm is advancing rapidly the halo brightens and narrows and the stars fade. This is proof to show that the proverb stating that the number of stars inside the ring is a forecast of the number of days of storm is sheer nonsense. For presently the ring closes and the stars disappear which would show according to the proverb that the storm had changed its mind and would cut down the number of days from several to none.
The moon grows paler. The light that it casts upon the earth is eerie at this stage. Within a few hours the coc.o.o.n of mist is completely woven about the moon. The circle has closed. Snow or rain begins within a few hours after the moon has entirely disappeared. If it does not so begin it shows that the process of increasing humidity is a very slow one and the storm center is probably pa.s.sing far to one side of the observer. Also if the snow begins before the light of the moon is entirely suppressed the disturbance is a shallow one and the storm will be light.
When the halo is actually a corona (red outside) the approach of the storm can be gauged by the rapidity with which the circle grows smaller. For a decrease in diameter denotes that the size of the moisture drops is increasing and therefore the storm is approaching. As a matter of fact the corona will have disappeared long before the time for rain. Still it is useful to know that if the corona increases in size the conditions are clearing. With the halo the reverse holds. For when the clouds are very high the halo looks small, and high clouds imply swifter winds and a greater distance from the storm center.
The Zuni Indians who have an eye for the picturesque as well as for the truth state the chief fact about haloes happily: "When the sun is in his house it will rain soon." Another saying of theirs anent c.u.mulus clouds holds for our country as well as for theirs: "When the clouds rise in terraces of white, soon will the country of the corn-priests be pierced with the arrows of rain."
There are many little observations which the man who has kept the corner of his eye open may profit by and yet which are rather difficult to express in type. Who could describe an egg for instance whose springtide of youth was far behind and yet was not quite ready for the discard! In nature it is the fleeting moment of transition, the half-tones of the border that are so hard to catch, so difficult to portray, and yet so very important not to miss if one is to become sure. There follow some of the baldest and most communicable half-facts about the weather that should be used oftener to bolster up some opinion gleaned from more positive sources than to mould one in their own strength.
Moisture in the atmosphere helps sight to a certain extent. For when the air is full of moisture its temperature tends to become equalized, obliterating irregularities which would otherwise reflect the vibrations producing sight and sound. So if one hears better or sees better on a certain day it augurs a moister atmosphere,--an auxiliary sign if there is a view that you are fond of looking at many times a day. In the city, alas, clearer vision on one day than another means merely that less coal is being used. But in camp there is very often a perceptible difference in one's seeing ability even on days that could all be cla.s.sed as clear.
Another thing that the haunter of the woods may notice is that his smelling capacity is increased before a storm. The increase of humidity which precedes a rain buoys up odors and depresses smoke. Even in dry weather if you will stroll by a marsh you will notice how rank the vegetation smells and how the smells float in layers in the air strata of different humidity. One's sense of smell is a very slender thread on which to hang a storm, however.
Fires burn more briskly in dry air than in moist, but to tell the difference (if you can't feel it) you must be very sure that your wood is as dry on one day as on another.
Before a rain many plants close their flowers or shift their leaves. The dandelion, pimpernel, red clover, silver maple are good examples of this, but they would not be of much use in the North Woods. The closing, too, takes place only a few hours before rain and is merely confirmation of the signals rendered more adequately by clouds and winds.
Bugs and flies are particularly annoying before a storm and it is surprising that the spider should not take advantage of this to get a meal. But spiders are cautious and they never spin a web on the gra.s.s, at least on the day that brings a storm. The insects do not fly so high on these weather-breeding days and consequently the birds that feed on them fly lower. The chimney swifts are a particularly good guide to the different alt.i.tudes at which insects fly.
The stars are on a par with bugs as weather guides, although there are many proverbs that grant them much. One circ.u.mstance should not be neglected, however, and that is that wind mixes air and when air is well mixed atmospheric inequalities are less disturbing to vision. Hence when one can see the stars and the moon well wind currents are oftenest the cause. Even if it is not blowing on earth these wind currents may yet be blowing above to reach the earth later. In this way cold waves arrive. There is an old proverb about this condition, applying it to the moon, "Sharp horns do threaten windy weather."
But the stars are of second rate importance because they are so soon obscured. If you can't see them it is cloudy, but you do not know what kind of cloud it is. If only the brightest show, a veil of cirrus is arriving. A dark sky with only a few dim stars is an omen of storms. If the stars twinkle it is because the varying currents of the upper air are in juxtaposition. If they twinkle while the northwest wind is on it is a sign of colder weather,--not because they are twinkling but because of the northwest wind.
In the days when almanacs were the sole guides to the weather a man with a sense of humor, Butler by name, got out one and dedicated it to "Torpid Liver and Inflammatory Rheumatism, the Most Insistent Weather Prophets Known to Suffering Mortals." Rheumatism is following the almanac to the sc.r.a.p heap, and it would be harder for a camper to guess what a torpid liver was like than to forecast the weather, yet for the majority of "suffering mortals" there is still much truth in the amiable observation of Mr. Butler, "As old sinners have old points O' the compa.s.s in their bones and joints."
CHAPTER V.
THE BAROMETER.
Whatever the foregoing chapters may imply as to the whole world going camping the fact is that the woods are still, unfortunately, for the few. The woodsman must yield gracefully to the suburbanite,--in numbers.
But the weather is for everybody. To be sure the sunrise that talks so confidentially to the hunter of the coming day does not exist for the commuter. But the coming day does, even though the things it means are essentially different. To the hunter with his seasoned clothes and well-earned health a rain is only of concern in so much as it affects the business of the day; personally it is of small moment. But to the commuter what does the weather mean? Dollars and cents, of course. His business goes on, but to his person one unexpected shower = the cost of pressing a suit; one thorough soaking = one doctor's bill. For you cannot expect the man to throw off a chill who can quiet his conscience on the matter of daily exercise by watering the geraniums and reading the newspaper.
Weather wisdom is necessary for the hunter; for the commuter it pays.
The hunter had to rely on local weather signs. The commuter can go him one better by investing $10 (how finance will creep in!) in a little aneroid barometer. The local weather signs were good for twelve hours at the longest. The barometer is a faithful instrument that adds another twelve hours to a man's knowledge. Half a day, or even a day before any local sign of changing wind or growing cloud appears the barometer is on the job. It will register in Philadelphia the news of a disturbance approaching the Mississippi. So sensitive is it that it is the slave to every wave of the great air ocean.
The barometer gauges for the eye the amount of atmosphere that is piled above one. If the amount is normal and at sea-level the instrument will measure 30.00 inches. This air pressure is equivalent to a column of water 30 feet high. As this would make unwieldy prognosticators the scientists use mercury instead, which requires a column less than three feet long. And for general purposes this is supplanted by the handy little aneroid (which means "without fluid"). This is so fixed that the pressure of the air influences the upper surface of a vacuum chamber, balanced perfectly between this pressure and a main spring. This action is transmitted to an index hand moving across the dial marked into fractions of inches after the manner of the recognized standard, the mercurial barometer.
When the warm moist light air of a cyclone invades a locality the pressure is partially removed, the vacuum chamber is not pressed so hard and the dial hand or the mercury subsides. When the cold, dry, heavy air of the anticyclone lumbers in more pressure is applied and the mercury, or the dial hand, climbs. So a falling barometer means a storm, a rising one fair weather.
That is a generality that glitters. If that were all there was to it weather officials would have a sinecure. But each cyclone varies in size, intensity, and rate of progress. Some do not advance for days. Therefore there has grown up a pretty large body of information as each storm has had to be watched and the barometric movements recorded. The most important variations follow: Remembering that 30.00 inches is sea-level normal, if the barometer is steady at 30.10 or 30.20 the weather will remain fair as long as the steadiness continues, and on the turn, if the fall proceeds slowly with the wind from a westerly direction fair to partly cloudy weather with slowly rising temperature will follow for two days.
If the barometer rises rapidly from 30.10 the fall will be equally rapid and rain or snow may be expected within a couple of days. Since the depressions of the atmosphere tend to a certain regularity about the center of the storm it follows that the reactions will follow the actions in similar manner,--a long rise portending a long fall and a variable gla.s.s meaning unsettled conditions.