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READING THE WEATHER
[Illustration: SHOWER BEHIND VALLEY FORGE
_Courtesy of Richard F. Warren_]
READING THE WEATHER
by
T. MORRIS LONGSTRETH
Illustrated with Photographs by Richard F. Warren
Outing Handbooks
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
CHAPTER PAGE
FORECAST i
I OUR WELL-ORDERED ATMOSPHERE 11
II THE CLEAR DAY 20
III THE STORM CYCLE 42
IV SKY SIGNS FOR CAMPERS 64
THE CLOUDS 65
THE WINDS 76
TEMPERATURES 86
RAIN AND SNOW 99
DEW AND FROST 112
THE THUNDERSTORM EXPOSED 116
THE TORNADO 129
THE HURRICANE 133
THE CLOUDBURST 139
THE HALO 140
V THE BAROMETER 147
VI THE SEASONS 157
VII THE WEATHER BUREAU 167
VIII A CHAPTER OF EXPLOSIONS 175
CONDENSATIONS 185
SIGNS OF FAIR WEATHER 185
SIGNS OF COMING STORM 187
SIGNS OF CLEARING 189
WHEN WILL IT RAIN? 190
SIGNS OF TEMPERATURE CHANGE 191
SOME UNSOLVED WEATHER PROBLEMS 192
WHAT THE WEATHER FLAGS MEAN 193
OUR FOUR WORLD'S RECORDS,--AND OTHERS 195
ILLUSTRATIONS
Shower Behind Valley Forge _Frontispiece_
PAGE
Cirrus Deepening to Cirro-Stratus 16
Cirro Stratus with Cirro-Cumulus Beneath 32
Cirro-Cumulus to Alto-Stratus 48
Alto-Stratus 80
Cumulus 96
Stratus 128
Nimbus 160
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 deg. below zero eternally
prevails--459 deg. 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.
[Illustration: 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.