SKY SIGNS FOR CAMPERS
The weather-wise, even more so than poets, are born. But that only goes to
say that weather-wisdom can be fathered. For poetry and canoeing and the
art of making fires, once the desire for these things is born, may be
aided infinitely by observation and practice. Nobody can teach a man the
smell of the wind. But the chap who feels nature beating under his heart
can, by taking thought, add anything to his stature. So it is with those
who are called weather-wise. An unconscious desire, a little conscious
knowledge, a good deal of experimentation with the cycle of days, and you
have a weatherman.
These chapters aim to put the little conscious knowledge into the hands of
the people with the unconscious desire, so that when they take their week
in the woods for the first time (and their month for the second time) they
may enjoy the shifting scenery of the sky-ocean and, incidentally, a dry
skin. For I take it that everybody will soon be camping. Maine and the
Adirondacks have become a family barracks. It is Hudson Bay for bachelors.
And over this expanse of woods and children the weather problem ranks with
the domestic one. For naturally if a soaking would endanger his vacation
the husband must not permit a rain,--unexpectedly. In all seriousness, it
is of avail to know the skies if one is going into the wilds just as it is
of avail to know what severed arteries demand, what woods burn well, and
what mushrooms can be eaten, even though one can get along without knowing
these things until perchance the artery is severed or the arched squall
catches one far from shore.
At the very least, one grain of weather wisdom prevents a mush of
discomfort. And if, fellow-camper, the following observations gathered on
a thousand thoughtless walks do not tally (for the northeastern states)
with yours, write me, so that in the end we may finally contrive together
a completer handbook of our weather.
THE CLOUDS
Clouds are signposts on the highway of the winds. Every phase of the
weather, except stark clearness, is commented upon by a cloud of some
sort. When danger is close they thicken. When it passes they disappear.
The aviators of the future will be cloud-wary. He who flies must read or
never fly again.
The cirrus cloud is always the first to appear in the series that leads up
to the storm. It looks like the tail of Pegasus and for it the old
forecasters in their forecastles made a special proverb.
"Mackerel scales and mares' tails
Make lofty ships carry low sails."
These white plumes and scrolls which are in reality glistening ice-breath,
fly at the height of five, six, seven, and even eight miles. And as a sign
of coming storm they are about as infallible as anything may be in this
erratic world. They were born in the cradle of a storm. The storm center
was breathing warmed air upward to great heights, and although the disc of
the storm itself was only two or three miles deep, its nucleus,
crater-like, shot warm columns twice as far. With just enough moisture
content to make a showing against the blue these streamers flowed to the
eastward. At those dizzy heights the prevailing westerlies are in full
force, blowing from eighty to two hundred miles an hour night after night
and day after day. These westerlies caught the storm exhalations, the
streamers, and hurled them eastward at greater speed than the main body of
the storm. And that is the reason that we see these cirrus clouds always
eight, mostly twelve, often twenty-four and sometimes forty-eight hours
before the storm is due.
Just a few strands of cirrus have little significance. They may be
condensation from a local disturbance, or a back fling from a past storm.
But if the procession of the cirri has some continuity and broadens to the
western horizon it is a sign about eight times in ten that a cyclone is
approaching. Occasionally the storm center is too far to the south or
north to cause rains at your locality, but the cirri bank up on the
horizon and their lacework covers the sky. If they appear to be moving
toward the region of greatest cloudiness it is not a sign of
precipitation. This condition is most apparent at Philadelphia when the
storm center over Alabama or Mississippi floats out to sea by way of
Florida without having the energy to turn north. Then the cirrus is seen
thickly on our southern horizon. Looking closely one sees that the cirri
are moving from the northwest, and are being drawn into the storm area
instead of proceeding in advance of it.
Careful watching will sometimes enable one to tell whether the tails are
increasing or decreasing in size. If they dissolve it means that the
cyclone from which they were projected is losing strength because of new
conditions. Cloudiness may follow but no precipitation of consequence. The
plumy tails are expressive: pointing upward they mean that the upward
currents are strong and rain will follow; pointing downward they mean that
the cold dry upper currents have the greater weight and clear weather is
likely. In summer the cirrus cloud formations are not such certain advance
agents of rain because all depressions are weaker and less able to
confront a well-intrenched drought. As the proverb goes, "all signs of
rain fail in dry weather," and there is some truth in it.
The fine wavy cirrus clouds often increase in number, develop in texture
until the blue sky has become veiled with a muslin-like layer of mist.
This is the cirro-stratus, and is a development of the cirrus, but it does
not fly so high. Its significance is of greater humidity and is the first
real confirmation of the earlier promise of the cirri. Another form that
the cirro stratus may assume is the mackerel sky,--clouds with the light
and shade of the scales of a fish. If this formation is well-defined and
following cirrus it is a fairly accurate storm indicator. It is not quite
infallible, however, as the same forms may be assumed when the process is
from wet to dry.
The old proverb, "Mackerel sky, soon wet or soon dry," expresses this
uncertainty. If dry is to follow the scales will appreciably lessen in
size and perhaps disappear. If the cirro-stratus or scaly clouds are
followed by a conspicuous lowering it is only a question of a few hours
until precipitation begins. The cirro-stratus at a lower level is called
alto-stratus and this becomes heavy enough to obscure the sun.
The cloud process from stratus on is slow or rapid, depending upon the
energy of the coming storm and the rate of its approach. In most cases the
clouds darken, solidify, and become a uniform gray, no shadows thrown, no
joints. Soon after the leaden hues are thus seamless the first snowflake
falls. If it doesn't it is a sign that the process of condensation is
halting: the storm will not be severe. Sometimes there is no precipitation
after all this preparation, but under these circumstances the wind has not
ventured much east of north. From the time that the snow starts the clouds
have chance to tell little. Only by a process of relative lightening or
darkening can the progress of the storm be followed and the wind, and not
the clouds at all, is the factor to be watched; for occasionally the sun
may shine through the tenuous snowclouds without presaging any genuine
clearing so long as the wind is in the east.
But in summer the clouds become even more eloquent than the wind. The
rain-cloud, called the nimbus, becomes different from the dull winter
spectacle. In summer air becomes heated much more quickly and the warm
currents pour up into the cold altitudes where they condense into the
marvelous Mont Blancs (or ice-cream cones) of a summer afternoon. These
piled masses of vapor are cumulus clouds, and if they don't overdo the
matter are a sign of fair weather. They should appear as little cottony
puffs about ten or eleven in the morning, increase slowly in size, rear
their dazzling heads and then start to melt about four in the afternoon.
But perhaps the upward rush of warm, moist air has been so great in the
morning that the afternoon cooling cannot dispose of it all without
spilling. Then occurs a little shower,--the April sort. Often in our
mountainous districts it showers every day for this reason. The great
thunderstorms come for greater reasons: they are yoked to a low pressure
area and represent the summer's brother to the winter's three-day storm.
Cumulus clouds are called fair weather clouds until their bellies swell
and blacken and they begin to form a combination in restraint of sunlight.
Even then it will not rain so much out of the blackness as out of the
grayness behind it, and if there is no grayness chances are that you will
escape a wetting. One can almost always measure the amount of rain that is
imminent by the density of the curtain being let down from the rear of the
cloud. If you can see the other clouds through it or the landscape the
shower will be slight. If a gray curtain obscures everything behind it you
had better pull your canoe out of the water and hide under it if time is
less valuable than a dry skin. Such showers may be successive but rarely
continuous.
Rain clouds have been observed within 230 yards of the ground. Very often
it can be seen to rain from lofty clouds and the fringe of moisture
apparently fail to reach the earth, because the condensation was licked up
and totally absorbed on entering a stratum of warmer air. The reverse of
this occurs on rare occasions;--condensation takes place so rapidly that a
cloud does not have time to form, and rain comes from an apparently clear
sky. This phenomenon has been witnessed oftenest in dry regions and never
for very long or in great amounts, although a half hour of this sort of
disembodied storm is on record.
If the cumulus clouds of the summer's afternoon do not decrease in size as
evening approaches showers may be looked for during the night. And if the
morning sky is full of these puffy little clouds the day's evaporation on
adding to them will probably cause rain. A trained eye will distinguish
between a stale and fresh appearance in cloud formation, the light, newly
made, fresh clouds, like fresh bread, contain more moisture. If the clouds
have much white about them they need not be feared as rain-bearers. Clouds
are much higher in summer than in winter and the raindrops of warm air are
larger than those of cool.
If cumulus clouds heap up to leeward, that is, to the north, or northwest
on a south or southwest wind a heavy storm is sure to follow. This is
notably so as regards the series of showers in connection with the passage
of a low-pressure area. The wind will bear heavy showers from the south
(in summer) for a whole morning and half the afternoon with intervals of
brilliant sky and burning sun. Or perhaps the south wind will not produce
showers, but all the time along the northwest horizon a bank of cloud
grows blacker and approaches the zenith, flying in the face of the wind or
tacking like a squadron against it. About the time that the lightning
becomes noticeable and the thunder is heard the wind drops suddenly, veers
into the west, and the face of things darkens with the onrush of the
tempest.
Although no rain may have fallen while the wind was in the southern
quarter yet that constituted the first half of the storm and the onslaught
of rain and thunder the second. While the storm area moved from the west
to the east the circulation of air about the center was vividly
demonstrated by the south wind blowing into the depression, whose center
was epitomized by the moment of calm before the charge of the plumed
thunderheads from the northwest.
Most camping is done either in hilly or mountainous country where the
movement of clouds is swifter and more changeable than over flat lands.
There is one sign of great reliability: if the mountains put on their
nightcaps the weather is changing for the wetter, and if clouds rise on
the slopes of the hills or up ravines, or increase their height noticeably
over the mountain-tops, the weather is changing for the dryer. In the
mountains where abrupt cliffs toss the winds with all their moisture to
heights that cool clouds form and condense rapidly and the weather changes
quickly. But even in the mountains the big changes give plenty of warning.
Often clouds may be noticed moving in two or even three directions on
different levels at once. The upper stratum will probably be cirrus from
the west. Cumulus or stratus may be floating up from the south. A light
drift of vapor called scud may fly on the surface easterly wind. Such a
confused condition of wind circulation betokens an unsettled system of air
pressures and as frequent collisions of the air bodies at varying
temperatures are inevitable rains, probably heavy, will follow.
On clear days one will be surprised to see isolated clouds, usually the
torn, thin sort, drifting across the sky from the east. A change will
follow soon.
In winter black, hard clouds betoken a bleak wind.
Clear winter days several times a season show a brilliant blue sky filling
with great cumulus clouds of dark blue, blurred at the top and gray at the
base. They will sprinkle snow in smart, short flurries, and are ushering
in a period of clear and much colder weather.
A sky full of white clouds and much light is a cheerful sign of continuing
fair weather.
The softer the sky the milder the weather and the more gentle the wind. It
is the dark gloomy blues that bring the wind. But do not mistake the
woolly softness of the rolling clouds before a thunderstorm. A sudden and
often violent gust follows. Tumbling clouds in any event should make one
wary of venturing on water. Summer drownings would not be so numerous if
the portent of the squall were heeded.
To this data might be added many singular cloud formations that are not
observed often. The funnel shaped cloud of the tornado, the green shades
of the hurricane cloud, the green sky of cold weather showing out between
layers of steel blue, coppery tints that show before heavy storms
sometimes, variations of color at sunset each of which has a meaning which
practice in deciphering will make clear. But enough has been given to show
sky-searchers how many are the tips of coming weather that may be read
from a conglomeration of fog particles. Nobody with eyes should be caught
unawares by day. The look of the sunset shadows forth much of the coming
night. And throughout all this truth holds: the greater the coming storm
the longer and clearer are the warnings given to the watchful.
THE WINDS
The wind is the ring-master of the clouds. It whistles and they obey.
Therefore to be windwise is to be weatherwise, almost.
One can get a hold on the wind by learning to gauge its strength. Look at
the trees or the smoke from your city chimneys and guess how fast it blows
at eight o'clock in the morning, or eight at night. The weather report the
next day will tell you how nearly you were right.
Beginning is easy; anybody can guess a calm. When the leaves are just
moving lazily the Weather Bureau calls it a light or gentle breeze, moving
from 2 to 5 miles an hour. A fresh breeze, from 6 to 15 miles will stir
the twigs at first and finally swing the branches about. From 16 to 25
miles, a brisk wind, will cause white caps on the lakes, tossing the tops
of the trees, but breaking only small twigs. Increasing from 26 to 40
miles it becomes a high wind that breaks branches on trees, wrecks signs
in the towns, causes high waves at sea and roars like the ocean in heavy
squalls through the woods. From 40 to 60 miles an hour makes a gale.
Sailing craft are now in danger. The pressure at 50 miles an hour is 13
pounds to the square foot, having risen from three-quarters of an ounce at
3 miles. This pressure becomes 40 pounds per foot when the wind reaches a
velocity of 90 miles.
At 60 trees are uprooted, chimneys may go, it is difficult to walk
against, the noise becomes very great but rather inspires than frightens.
As the gale increases from 60 to 80 (which velocity the Bureau rather
weakly calls a storm wind), danger rapidly increases. Trees are
prostrated, the uproar becomes terrifying, walking without aid is
impossible, the great ocean liners are in danger, the sea becomes a
whitened surface of driving spume that heaps up into piles of water thirty
or more feet high, windows are blown in and frame houses cannot stand much
greater velocities. Anything from 80 miles an hour up is well called a
hurricane. Everything goes at 100. At Galveston the machine that
registered the wind velocity blew away at 100.
They have better instruments now, and in many places velocities of over a
hundred miles an hour have been recorded. As high as 186 miles was
registered on the top of Mt. Washington, and in a single gust 110 at
Montreal. The great hurricane winds are most felt at a few of the exposed
places on our coasts. Cape Mendocino, on the Pacific, has 144 miles an
hour to its credit in a January hurricane. But enough destruction is done
at 90 miles. Fields are stripped of their crops, or leveled; houses are
demolished unless they are specially built, like the New York
sky-scrapers, to withstand much higher velocities. In the small whirling
storms called tornadoes the wind is estimated to reach a velocity of 200
to 500 miles, and nothing but the cyclone cellar will shelter one from the
fury of the elements when they are really unleashed.
The higher one goes the greater the velocity of the wind. On the top of
Mt. Washington 100 miles is rather common for hours at a time and 150 is
recorded now and then. That is only 6000 feet above Boston. If such a
force struck Boston for a minute it would be blown _en masse_ into the
Bay.
Velocities on land are less than those at sea, because of the resulting
friction from obstacles. Velocities in summer are lower (thunder gusts
excepted) than in winter. Since the wind is caused by differences in
atmospheric pressure, and that in turn by disparities in temperature,
winter holds the palm for greater velocities because the wide whirl of a
cyclone over the great plains may cause to mix air from Texas with a
temperature of 60 degrees with air from Montana of 30 degrees below zero,
while the summer temperatures in both states might easily be 80 degrees.
Throughout most of our land certain winds have always the same bearing
upon the weather and this correspondence is roughly the same over most of
the country. West winds, for instance, are an almost universal guarantee
of clear weather. The Pacific Coast and western Florida are the
exceptions.
Northwest winds bring clear skies and cool weather everywhere. In winter
in the north plateau section heavy snows arrive in advance of the severe
cold waves that come on these northwest gales.
North winds are the cold bearing ones. Clear skies prevail under their
influence.
Northeast winds are cold, raw snow-bearing winds in winter and spring and
bring chilly rains in midsummer.
East winds are the surest rainbringers of all for the eastern two-thirds
of the country, and are soon followed by rain with a shift of wind over
the other third. Their temperatures are more moderate than those of the
northeast storms.
The greatest falls of rain occur, however, with the southeast winds, whose
moisture content is greater than that of the others because they are
warmer and blow off water except in Rocky Mountain districts.
South winds are warm and contain much moisture, which falls in showers
rather than in continuous rains.
The southwest winds of winter precede a thaw and are much damper than west
winds. In summer over much of our country they are hot, parching winds
that injure vegetation.
The average velocity of the wind from these different quarters is variable
in different parts of the country, the severest being on the southeast and
northwest quadrants. The highest winds are always where the steepest
gradients are; that is, where the barometric pressure decreases or
increases the fastest. The steepest gradients are usually on the northeast
and northwest sides of the storm center, with the exception of the
Atlantic Coast where the southeast winds are often highest. The average
for the northeast quadrant is 16 miles, for S. E. 30, for S. W. 20, and
for the N. W. 30 miles an hour. But averages can deceive. As a matter
of fact single instances of great wind velocities occur from each point of
the compass. The greatest velocity ever recorded at Philadelphia occurred
in October, 1878, when the wind blew seventy-five miles an hour from the
southeast. But the record velocities for eight of the other months were
registered in the northwest quadrant.
[Illustration: ALTO-STRATUS
_Courtesy of Richard F. Warren_
Not so high as cirro-stratus, and yet partaking of the same skeiny
texture. This would be a normal sky in winter about six hours after the
veil of cirrus had begun to throw its haze about the sun. No other cloud
formations appear, however, and so the area of precipitation is still
pretty far away. In summer such a sky is less common. If the disturbance
is to amount to anything the cirro-cumulus will soon form. If the wind is
from a westerly quarter the blanket of cloud is doubtless a drift from
some distant storm, which will not affect this locality. The wind is
always blowing toward a storm and away from clear weather.]
The period of time when the barometer is beginning to rise after having
been very low is that when the strongest winds blow.
Some sections of our country have special kinds of wind that are
peculiarly their own, notably Colorado, Wyoming, and Montana where the
chinook reigns. This phenomenon belongs only to the cold season and only
to the coldest days of it. It is a warm wind that begins to blow without
much warning from the southern quarter. It is caused by a body of cold air
suddenly falling from a great height. As it falls its descent heats it and
it causes a rise in the temperature of the surrounding locality that
greatly exceeds any rise from other causes. The increase in temperature
will be as much as forty degrees in fifteen minutes.
This sudden dry heat is a great snow-eater. If it were not for the chinook
the snow-blanket would stay so much longer on the cattle ranges that they
would be useless as such. In northeastern sections of our country and
Canada the warm winds blowing in from the ocean at the approach of a
cyclone do away with the snow rapidly but with nothing like the speed of
the chinook.
Another phenomenon of the air that is of tremendous benefit to man is the
sea-breeze. During the intense heat of a hot wave the wind may shift to
the east in Boston and in fifteen minutes coats are comfortable. Such a
shift may bring relief to a strip of land two hundred miles wide along our
entire eastern seaboard. The sea-breeze is explained by the fact that the
land cools more quickly than the sea and also warms more easily. During
the whole forenoon of a summer's day the sun has been pouring upon land
and sea, but the land-air has become much hotter than the air over the
sea. It rises and the sea-air rushes landward. By midnight the land has
cooled off even more than the sea and the heavier air now presses out to
sea again. On every normal day this balancing process takes place.
If it doesn't conditions are abnormal and chances are that mischief is
brewing. This ebb and flow of warmer and cooler air is, on a small scale,
exactly what is happening on a vastly larger field of operations between
cyclone and anticyclone. And it is the dominance of the anticyclone with
its prolonged rush of air from the northwest that interrupts the sea
breeze for two or three days in winter, as the cyclone prevents the night
land breeze from taking place when it is central off the eastern coast.
The exchange of air between mountain side and valley is similar to the
land-and-sea breeze. The rarer air on the mountain side heats faster by
day and cools faster by night than the denser air in the valley. Therefore
during the day it rises and the valley air rushes up to take its place;
during the night it cools and sinks into the valley. This is a great help
when one is shut up in a secluded valley for several days and cannot get a
good view of the skies. The atmosphere is acting properly and will remain
settled so long as the air blows up your ravine for most of the day, and
turns about sundown and blows out and down the ravine like a flood of
refreshing water.
Of course many valleys are so large as to be affected, not by these local
causes, but by the larger movements of the anticyclones when the
sure-clear west wind may blow up the valley for three days at a time. But,
nevertheless, for most mountainous places the logic holds and you may
expect rain if the wind does not blow coolly down the ravine at night. Of
course watch your clouds for confirmation.
In times of calm prepare for storm. An eminent meteorologist has frowned
upon me for saying that. It is not the whole truth, I admit, but there is
a certain kind of calm which happens often enough to justify the remark.
It happens this way. A severe storm has passed. The customary anticyclone
with its brisk northwest winds has arrived and is blowing with all the
vigor necessary to induce one to believe that the clear weather is to
continue for the usual length of time; that is, three or four days. But
suddenly in the early afternoon, just when it should be blowing its
hardest, the wind drops, lulls, shows a tendency to change its direction.
There is only one explanation. Another cyclone has developed off in the
west. It has knocked the anticyclone on the flank, taken the teeth out of
the gale.
The wind shows this before clouds can. The absence of wind when there
ought to be a lot shows it before even the first cirrus swims overhead.
The chance is that when the flow of anticyclonic air has been thus rudely
cut off and stillness follows, it will be storming by morning. It is best
to keep an eye on these abnormal, precipitous calms. In times of peace
prepare for rain.
But the eminent meteorologist was eminently right when he said that the
statement was misleading unless explained. For there are many kinds of
calms that do not portend coming storms. Nearly every day, winter and
summer, but particularly in summer, the wind drops to a calm at sunset.
That is a time of adjustment. After sunset when the accounts are all in
the wind springs up with as much force as it had in the afternoon and
continues until dawn. At sunrise, however, there is another truce. If this
truce is neglected either at sunrise or at sunset it is a sign that either
a cyclone on an anticyclone is very much in the ascendency. These truces
are most often observed at the seashore when you are out sailing and the
smell of supper fills your nostrils but is not sufficient to fill your
sails. These calms are normal and the best sign of a fair day on the
morrow, provided the other signs agree.
During the great transition period from summer to winter comes that
autumnal truce, Indian Summer, which is the chief claim to fame of
American weather. For day after day a brooding haze sleeps in the air,
sometimes for weeks there is no wind of any strength. Winter advances
insidiously in the fall but retreats in commotion, and the cooling off
process permits of these still days while they are uncommon in the spring.
The wind checks off more mileage in March than in any other month.
While the regular day's end calm and the calm of the year's exhaustion
mean continued fair weather, there is one calm that everybody knows, which
is the most dramatic moment in the whole repertory of the weather: the
foreboding, ten-count wait before the knockout blow of the thunderstorm.
But when that calm comes every one is already sitting tight so that it is
not much account as a warning. They say that the intense stillness before
the hurricane strikes is uncanny.
Whether inshore or afloat the wind is to be watched if you would know what
weather is to be. It is only another of Nature's paradoxes that the most
unstable element should be the most reliable guide of all on the uncertain
trail of the next day's weather.
TEMPERATURES
Considering that the temperature of the sun is 14,072 degrees Fahrenheit
and the temperature of space is absolute zero, 459 degrees below ours, we
do very well on earth to be as comfortable as we are.
And we owe it all to the atmosphere which keeps the sun from concentrating
upon us. Our place in the sun is so very small that we intercept only
one-half of one billionth of the heat which it is giving off night and
day. But that is sufficient to do a lot of damage if it could get at us.
But even the paltry range of temperatures so far recorded on our
planet,--from 134 degrees above zero one day in California, to 90 degrees
below zero one night in Siberia,--is by no means a fair statement of the
extremes we are called upon to bear. Only twice a decade in our country
does the mercury vary as much as sixty degrees in twenty-four hours, and
there are vast areas where the daily change amounts to only a few degrees.
The changes that do come so suddenly to us, particularly in winter and
that are known as cold waves, are in reality beneficial. To them we
Americans may owe our energy, our vivacity, our changeability of mood. The
refrigerated, revivified air sweeping down from the north is tonic. It is
heavy, and issuing from antiseptic altitudes, drives the humid,
germ-nursing air from our city streets. If we had arranged a process of
refreshment like this at vast expense we should have been intensely proud
of it. As it is we are intensely annoyed at it and occasionally a few
people are frozen to death. The Weather Bureau warnings and the coal clubs
are reducing the loss in property and lives.
If you are sleeping out it is of great importance to know when the mercury
is going to take one of these swoops, for sleeping cold means little real
rest because one's muscles are tense, and the next day's packing needs all
the relaxation one can get. Two generalizations govern pretty much every
change of temperature: the mercury will rise before a storm and it will
fall after one, winter and summer, but much more conspicuously in winter.
There are two reasons for this. Our cyclones usually cross our country
over such a northern track that over most of the country the air drawn
into them comes from the southern quarters and is therefore warmer than
the air previously flowing from the anticyclone. Also the process of
precipitation causes heat. This is true to such an extent on the coast of
Ireland where it rains most of the time that a scientist has computed that
the inhabitants get from one-third to one-half as much heat from the
rainfall as they do directly from the sun. Thus a normal storm is doubly
sure to warm up the environment.
In summer the reverse is partially true, for very often the rain does not
begin until the actual center of depression has passed and the west winds
have begun to exercise their cooling influence. So that in summer we have
a sultry, sunny day as the first half of the storm area and then a cooling
shower. Also after two or three days of warm weather in spring and autumn
we have a rainstorm of the winter type which lowers the temperature
instead of raising it. This is because the heat produced by the storm is
less than that of the sun's rays intercepted by the clouds. The clear
skies of the preceding anticyclone had permitted the land to warm up very
fast under the midsummer sun, and the clouds of the cyclone, by cutting
off the supply, had made a relative chill.
In winter the sunrays are so much feebler because of their slant and
radiation proceeds so rapidly under the dry air of the anticyclone that a
much greater degree of cold is produced than when the cyclonic clouds
prevent the radiation. Therefore the rainy area is the warmest of all.
Even in summer the winds from the southeast, south, and southwest are
warmer than those from the opposite quarters, not only because they blow
from a quarter naturally warmer on account of the sun, but because they
are surface winds and have absorbed some of the heat from the soil. Being
denser, they absorb it more readily and hold it longer.
The change, then, from the period of fair weather to that of storm brings
an increase of temperature. But the rate of increase varies. The faster
the storm is approaching the faster the temperature will rise; and the
route of the storm's center makes all the difference as to the amount of
the rise. If the wind shifts by way of the north and holds in the
northeast until precipitation begins the rise in temperature will be very
slight. The great snowstorms of the northern half of the country occur
under just such a circumstance. If the wind shifts by way of the north but
gets around to the east or even southeast before the precipitation starts
the rise in temperature will be more pronounced, as much as thirty degrees
sometimes in a few hours, and the winter storm that started in as snow
soon changes to sleet and rain.
If the wind shifts by way of the south and then into the southeast the
rise will be vigorous and the storm will likely be a comparatively warm
rain. If the wind shifts only so far as the south the rise will be highest
of all and blue sky will often appear between the showers, showing that
the air is heated to a considerable height.
The progress of the temperature changes from the maximum of the cyclonic
area to the minimum of the anticyclone is also dependent upon the wind. If
the storm center is passing south and the wind begins to pull into the
northeast and north the temperature will fall steadily and slowly. The
rain or snow often cease gradually by the time the wind has reached the
north, but the temperature continues to fall slowly until it reaches very
low levels in mid-winter. If the storm center is passing north of you the
wind which has brought most of the rain while it was in the southeast with
comparatively high temperatures swings into the southwest, the temperature
falls somewhat.
There is usually a final downpour and a rapid shift of the wind into the
west or northwest, but almost never directly into the north. The
temperature falls several degrees in a few minutes, quite unlike the
gradual decline of the northeast-by-north shift, and clear skies come at
once with rapidly diminishing temperatures. In the vicinity of
Philadelphia a fall of twenty-five degrees would be most unusual on the
northeast shift,--such storms reaching 38 degrees and falling to 15,
while with the other shift a fall from 55 degrees to 15 would not be
unusual. Of course any one set of figures given could only show the
tendency and not the rule or limits.
After the manner of the wind-shift the intensity of the storm is a good
gauge of the temperature change to be expected by the camper. As a rule
the greater the intensity of the storm the greater will be the degree of
cold that follows it. The storms that have a complete wind circulation
about them are always more severe than those with incomplete circulation
and are invariably followed up by some reduction in temperature. If the
decrease is not proportionately great and the subsequent wind has only a
moderate clearing quality look out for another cyclone.
In such a case the temperature is the best witness of the contemplated
change. For instance, after a summer thunderstorm a decided coolness is
_de rigeur_. If this does not occur it means nearly every time that there
is another thunderstorm in process of construction. There may be not a
cloud in the sky, there may be no wind (although there should be) so that
the course of the thermometer is the only means of telling what is to be
the next event. Anybody can take a thermometer with him although a
barometer--the most accurate forecaster of all--may be thought too much
expense and bother.
At some future date the Weather Bureau will be able to predict the
temperature of seasons in advance. This, together with the amount of rain
scheduled to fall, will be an invaluable aid to everybody and to the
farmers most of all. At present mild seasons that have severe storms
without the appropriate degree of cold after them cannot be entirely
explained, let alone being prediscovered. They all hinge upon the more or
less permanent areas of high and low air pressure over the oceans and
international meteorological service has not progressed far enough to
support many ocean stations as yet.
Sometimes clear weather may intensify, growing brighter, stiller, colder.
This is because the pressure is increasing. Cold seasons are distinguished
usually by a succession of anticyclones. There is no way of telling how
long a certain spell of cold weather is to last, but I have noticed that
the same characteristics rarely predominate for longer than a month at a
time. In other words, if December has been warm and rainy, January will
likely be cold and dry. Of course, that is precisely the unscientific sort
of generalization which the Bureau very rightly frowns upon, but which
one may nurse privately until science has provided a substitute as she
already has in so many instances.
With a little practice it is an easy matter to estimate the temperature to
within a very few degrees. Try guessing for a few mornings and then look
at the thermometer. You will hit within three degrees every time after a
week of this.
Allowance must be made for the amount of moisture in the air and for the
force of the wind. Damp air feels colder by several degrees than crisp,
dry air, and a breeze increases the difference still more. Air in motion
is not necessarily colder than calm air. As a matter of fact the lowest
temperatures of all are recorded about sunrise after a still, clear night.
The amount of radiation accomplished during the last hours of the night is
amazing, and the downward impetus of the thermometer is often carried on
for an hour or more after the sun has appeared above the horizon. A
self-recording thermometer is an amusing toy which will show this and
becomes a valuable instrument if one raises fruit.
In winter three o'clock of an afternoon sees the highest temperature
usually, and in summer this maximum occurs as late as half-past five, due
to the fact that the sun can pour in its heat faster than the earth can
radiate it off. For the half hour before and after sunset, particularly in
winter, the loss of heat is relatively greatest; then the pace slackens
till three or four in the morning, when the plunge of the mercury is
accelerated until the rays of the rising sun counteract the radiation.
If the mercury does not rise appreciably on a clear winter's day it is a
sign that a cold wave is stealing in, due, doubtless, to a gradual
increase in pressure without its customary bluster. Very often snow
flurries predict its approach, but this may be so gradual that only the
restriction of the daily thermal rise may indicate it. By the next morning
the temperature will likely be twenty degrees colder.
If the mercury does not fall on a clear winter's night it is a sign that a
layer of moist air not far above the surface of the earth is checking the
normal night radiation. Unsettled weather is almost sure to follow unless
this wet blanket is itself dissipated and the mercury takes its customary
tumble before morning.
If the temperature falls while the sky is still covered with clouds
clearing, possibly after a little precipitation, will soon follow.
Hot waves approach insidiously. A night will not cool off as it properly
should, the sun will rise coppery, and while the day is yet young
everybody begins to realize that all is not exactly right. But the heat
increases usually for several days, not only by reason of steadily
lowering pressure, but also by accumulation. Finally when a climax is
reached it departs abruptly on the toe of a thunderstorm.
A cold wave reverses the process. It arrives abruptly on the heels of a
departing cyclone and, after losing power, steals away without any
commotion whatever. Its rate of progress is in close relation to the
cyclone ahead of it.
Our mountains play a great part in our weather. They are a right arm of
Providence to our agricultural communities. Due to their north and south
trend a cold wave of any severity reaches the Pacific Coast only once a
generation. Just once has snow been observed to fall at San Diego and it
is so rare south of San Francisco that many people never have seen a
flake. East of the mountains the belt of desert makes natural crops
impossible for a thousand miles, but if they crossed the continent all the
territory north of them would have such a cold climate that none of the
present enormous crops of Canada and our northern states could possibly be
grown. It is also due to the wide insweep of winds from the Gulf that
the plains states are so well watered.
[Illustration: CUMULUS
_Courtesy of Richard F. Warren_
The tops of cumulus are irregular, looking like wool-packs; the bases are
flat. The true cumulus shows a sharp outline all the way round. Its shape
is in constant change due to the strong winds it is encountering. It is
caused by the swift uprush of warm air on a sunny day. This cloud is a
sign of fair weather, because the base is not large, compact, or dark
enough to threaten rain and its comrades are also disjointed. If the
cumulus grow darker toward the horizon and increase toward evening a
squall is likely.]
In lesser fashion the Appalachians protect the Atlantic seaboard. They
withstand the impact of the cold waves to a great extent, although they
are not high enough to divert the flow of cold air entirely toward the
south and it is not desirable that they should. As things are the cold
strikes Alabama before it hits New Jersey, and is often more severe there.
Comparative cold is often registered by the green color of the sky. A
fiery red continues the prevailing heat.
The day that is ushered in by a fog, in summer, will likely be warm,
providing the fog lifts by ten o'clock.
The temperature of a night with even a thin covering of clouds will be a
good deal higher than if the sky is clear. In the British Isles the whole
difference between freezing and no freezing lies with the fairness of the
heavens. Everywhere frost will not form while the sky is covered, although
the temperature may be below the freezing point. In summer radiation on a
still clear night may be so rapid that frost may follow a temperature of
fifty degrees at nightfall.
The temperature at the surface of the earth may easily deceive, as a
colder or warmer stratum of air may overlie that immediately next to the
ground. I have seen water particles fall when the temperature was as low
as 16 degrees above zero, showing that the stratum of cold air was very
thin. Our sleet storms in which immense damage is done to trees and
telegraph wires occurs from just such a situation,--a cold, shallow layer
of air close to the earth, with the warm moisture-bearing air flowing over
it. The reverse of this situation is not uncommon--the sight of a
snowstorm proceeding merrily along with the ground temperature at 35 or
even 40 degrees.
Coming warmth may be noticed by the increase in size of snow flakes, with
finally hail and rain. Coming cold is foreshadowed by hail mixed with the
rain and lastly snow flakes which have a tendency to decrease in size.
Colors of the clouds predict temperature changes, but it takes much
practice to distinguish the cold, hard grays from the soft, warm ones. A
warm sky is always less uniform in color than a cold one. The colors of
winter sunsets are, as a rule, much brighter than those of summer skies.
The stars seem brighter on a night that is to be cold. If they twinkle it
is because of rushing air currents, and if the wind is from the northwest
the result may be a subsequent lowering of temperatures.
The whole question of whether it will be colder and how much is vital to
the camper and if the signs of change are taken along with the look of the
clouds and the direction of the wind he need never be wrong as to the
direction the mercury is going, and will soon be able to guess the
distance pretty fairly.
RAIN AND SNOW
East of the Mississippi River rain falls with the utmost impartiality upon
every locality. Thirty to fifty inches are delivered at intervals of three
or four days throughout the year. And if there is a slight irregularity in
delivery one can be sure that from 125 to 150 of the 365 days will be
rainy. Occasionally there is a more or less serious hold up of supplies,
but this rarely happens in the spring of the year and never happens to all
sections at once. And if there is a desire to make amends for the drought,
we have what we call a flood and blame it on the weather instead of on our
precipitous denudation of the watersheds.
West of the Mississippi particular people have to go to particular places
for their rain. If they like a lot of it they must go to the coast
districts of Washington or Oregon where they can have it almost every day.
It rains a good deal at Eastport, Maine,--about 45 inches a year; that is,
nearly an inch a week,--but at Neal Bay, Washington, at about the same
latitude, in one year it rained 140 inches, and it never stops short of
100 inches any year.
On the other hand, if the Washington people are tired of it they need only
escape to Arizona where it rains about two inches a year, and they can
live in an enterprising hotel down there whose manager believes that it
pays to advertise the sun. He guarantees to provide free board on every
day that the sun doesn't shine.
In the plateau section enough snow falls every year to store up enough
water for irrigation purposes, and the little rain that falls arrives in
just the right season to do the most good, the spring. In California what
the farmers lose in amount they make up in the regularity of its arrival.
North of the Ohio River most of the precipitation from November to April
is snow. About 50 inches of it falls on the average over this tremendous
territory. And it is more useful than rain,--the handy blanket that makes
lumber-hauling easy, that keeps the ground from freezing to Arctic
depths, that fertilizes the soil, and that acts as a great reservoir,
holding over the meat and drink of the vegetable kingdom till the thirsty
time arrives. In upper Michigan and Maine the average depth becomes 100
inches. Averages are very misleading when snowfall is being considered,
some winters producing very scanty amounts and others heaping it on to the
depth of 185 inches once at North Volney, New York.
South of the Ohio the depth varies from substantial amounts in some
winters to almost nothing in others. Snow has been observed, however, in
every part of our country except the extreme southern tip of Florida. Once
and only once on the records a great three-day snowstorm visited all of
southern California, extending to the Mexican border and to the coast.
The strip of country between the parallels of New York City and Richmond
comprises the section wherein each winter storm is one large guess as to
whether the precipitation is to be snow or rain. A compromise is usually
affected in this way. Before the clouding up began the mercury may have
stood at ten degrees below zero. As soon as the wind acquired an easterly
slant the temperature increased. As it neared the freezing point the snow
would begin, first in flakes of medium size which would enlarge until
after a particularly heavy fall of a few minutes they would at once almost
cease. Hail soon would succeed, the mercury still rising, and often the
hail would have turned to rain before the freezing point of the air of the
immediate surface of the earth had been reached, turning the snow already
on the ground to slush and making a holiday for germs.
One can always tell when this change to warmer is about to occur because
the clouds which have been part and parcel with the obscuring snow
suddenly show, not lighter but darker. The sudden increase in size of the
flakes is another infallible symptom of increasing warmth in the
atmosphere for each large flake is a compound of many smaller ones. When
the temperature is low the flakes are very small, being grains and
spicules in the severe blizzards of the west and falling as snow-dust in
the Arctic. In the heavy storms of the guessing-belt the flakes are not
necessarily small.
I have noticed (in the latitude of Philadelphia) that our largest storms
begin very leisurely indeed with small and regular-sized flakes. A quarter
of an inch may not fall in the first hour. As the center nears the snow
comes ever faster and larger, but not large, flakes are mixed with the
original-sized flakes. Snow dust is apparent. At the height of the storm
flakes of all sizes except the very large are falling, denoting great
activity in the strata of air within the storm influence. In the ordinary
storm an accumulation at the rate of an inch an hour denotes a storm of
considerable intensity.
The snow will likely keep on falling as long as the flakes are irregular
in size. If they grow large and few or very small a cessation is likely,
even though the wind is still blowing from an easterly quarter. The amount
of snow likely to fall can be gauged not only by the process of
flake-change but by the rate at which the wind rises. A storm's intensity
is measured by the amount of wind. A storm can be a storm without a drop
of rain or flake of snow if only there be enough wind. And as long as the
wind in a snowstorm keeps rising the storm is likely to go on, probably
increasing in volume of precipitation.
If the wind shows a tendency to edge around to the southeast there is
danger of the snow turning to rain; if the wind veers slowly to the
northeast the temperature will fall slowly and the rate of precipitation
will likely increase for a while. In such instances the snow does not
continue to fall after the wind has swung west of north. Often clearing
takes place with the wind still in the north or even a point east of
north.
Contrary to superstition snow may begin to fall at any hour of the day or
night. But certain hours seem more propitious than others, owing no doubt
to the tendency of cooling air to condense. Three o'clock of an afternoon
and eight o'clock in the morning are favorite times, the one being the
hour of a winter afternoon when cooling is begun, the other the hour when
the coldest time is reached and condensation likely if at all. Of course,
one remembers storms beginning at nine, ten, eleven, and every other hour.
Storms that begin in the morning seldom reach much activity before three
o'clock in the afternoon, while those that begin then quickly increase in
intensity as evening draws near and the sun's warmth is withdrawn from the
upper air-strata. More snow falls at night than in the daytime, also. Snow
is more delicate than rain and perhaps more responsive than rain to the
subtle changes of the atmosphere. Possibly there is no ground on the
Bureau records for these ideas, possibly storms have a tendency to start
from the Gulf on their northeastward journey and so reach Philadelphia
oftener at one time than another. I would like my notions confirmed that
snowstorms increase at nightfall, and that they prefer to start operations
at sunrise and about sunset.
For the camper the snowstorm need have no terrors. It gives a long warning
of its approach. It comes mostly without destructive winds. Its upholstery
protects and warms the walls of one's tent. It adds beauty to the leafless
woods, interest to the trailer, and a hundred amusements among the hills.
But the value of snowy weather is not only measured by its beauties and
commercial uses. There is another way: make it read character for you.
Watch the reactions toward the first snowfall of half a dozen kinds of
people. It will show you what they are; give you a very fair measure of
their youth.
Our atmosphere contains a lot of moisture that never gets precipitated.
You can prove this on any warm day by noticing the way the atmosphere acts
toward a glass of ice-water. When the air of the room is much warmer than
the surface of the glass it surrenders its moisture willy nilly. Sometimes
this condensation is enough to cause a miniature rainstorm that trickles
down the outside of the tumbler. If a small cold surface can wring so much
water out of a little air it is small wonder that we get an inch or so of
rain from vast currents of air at unequal temperatures.
Try to visualize the process. A stream of vapor has been warmed and is
ascending. A mile up and it has cooled not only by the reason of altitude
but also by the process itself. About each little dust-particle in the
surrounding area vapor forms--vapor cannot form without something to form
on, there being always enough dust from deserts and volcanoes to go round.
If the cooling proceeds the tiny globules enlarge and as they increase in
weight they settle and fall. Falling, they unite with others.
If the air-strata are very warm and thick the drops may grow to a very
considerable size. We see these in the middle of our great winter rains
when the insweep of southern winds with all their warmth and moisture is
very extensive. Also the first few drops that come from the thick, hot
lips of the thundercloud are usually immense.
The best way to measure the size of a raindrop is to have it fall in a box
of dry sand. It rolls up the sand and measurements can be easily and
accurately made. But the most interesting way is to let the first drops of
the thunderstorm fall upon a sheet of blotting paper. If the same sort of
blotting paper is used the measurements will be of just as much importance
for comparison. Circles as big as teacups are formed sometimes.
Heavy drops in winter mean a heavy fall, because they denote high
temperatures which are uncommon and are bound to be followed by
considerable condensation as the cooling proceeds back to normal
temperatures. Small drops in summer mean either cooler weather, or sudden
condensation. Small drops in winter are a sign of very thin
moisture-bearing strata, or low temperatures, indicating that the rain
will be light, protracted, and liable to change to snow.
Hail is frozen rain. Winter hail is small and harmless and rarely falls to
any depth because the exact temperatures that bring forth the hail rarely
continue for very long at a time. Hail in winter is merely the stepping
stone to either rain or snow. But in summer hail is a serious matter. It
shows that there is a violent disturbance of the atmosphere in progress.
Vertical air currents, probably abetted by electricity,--the authorities
are not sure--often carry the stones up several times. They take on layer
after layer, coalesce, and sometimes fall the size of eggs, apples, or any
other fruit, barring melons. The usual summer hail does not exceed the
size of a robin's egg. Even a projectile of that size, however, falling
for a half mile or more has a tremendous destructive power. Greenhouses
suffer, birds are killed, cattle stunned, and loss of life has been known
to follow. In August in 1851 in New Hampshire hailstones fell to the
weight of 18 ounces, diameter 4 inches, circumference 12 inches. In
Pittsburgh stones weighing a full pound have crashed down, and in Europe
where many destructive storms have occurred there are official records of
even greater phenomena. The lightning accompanying these hailstones is
usually very severe. A flake or ball of snow forms the nucleus of a
hailstone.
If a thundercloud looks particularly black or if it can be seen in
commotion think of hail and seek shelter. It is pretty difficult to
predict exactly when hail is going to fall in summer. It is a possibility
with every large storm, but a probability with only a very few during the
summer. It accompanies tornadoes.
In winter hail falls before a rainstorm, even when the ground temperature
precludes the possibility of snow; some lingering stratum of cold air has
ensnared the drops on their way down.
Snow is not frozen rain. It has an origin of its own. It is born in a
temperature consistently below freezing and on the condensation of the
invisible moisture becomes visible as a tiny crystal. These infinitesimal
crystals unite and form larger, hexagonal shapes, elongated or starry.
They are wafted along, sinking, all slightly differing one from another,
although forming a few types. These types have been photographed and
catalogued and very often the altitude from which the snow is coming may
be learned from their shape and design. But this branch of science is
young yet and confusing and the outdoor man has surer signs of the
vicissitudes of the storm, in the general size of the flakes, the power
and direction of the wind, the clouds and temperature. The possibilities
of flake-study as a means of forecasting are many and of value as is
anything that tends to unveil the secrets of the greater heights.
Snowflakes are so light that after the storm processes are over and the
sun has come out the residue may still float lazily to the ground.
The wild disorder of the snow flurry will only last a few minutes and
never leave much snow on the ground.
Snowstorms that come on the wings of the west wind may be severe, but they
will be short. They are unusual in the east, but sometimes the heaviest
snows of the western states come on the sudden cooling that follows the
shift to west.
Snowstorms arriving on a high wind last only a few hours.
Snowstorms that are long in gathering and increase to considerable
intensity continue a long while.
Those that follow a sudden clouding up are of no importance.
The snowstorms that leave on a high wind from the west or northwest are
followed by a cold wave. Those that continue after the storm wind has died
away are succeeded by calm, clear, and usually warmer weather.
In northern districts a snowstorm may be looked for after a period of cold
weather. In middle districts if the cold has been severe the reaction to
warmer may bring rain instead. In such cases generalities are of no use,
and the possibilities must be determined by the man on the spot. The best
conditions for snow through the middle districts are occasioned by an area
of low-pressure with its attendant precipitation crossing the southern
half of the country while the northern half is under the influence of an
area of high-pressure with its attendant frigidity. The cold air flows
into the southern storm with the result that the middle districts get the
northern quadrants of the storm which are the usual snow-bearing ones
instead of the southern rain-bearing quadrants that they would have got if
the center of the storm had pursued its usual course up the Ohio and down
the St. Lawrence.
If the storm has two centers, one over Texas and the other over Montana,
as is so frequently the case in winter, the subsequent high pressure will
come too late to affect the temperature of the zone of precipitation and
the latter will likely be rain in the middle districts. Sometimes the
cyclones cross the country on the Canadian border and enough warm air is
sucked over the line to give the inhabitants of Montreal a thaw and rain.
This happens to them only once or twice a winter. And even more rarely a
cyclone over the Gulf with an anticyclone above it will give the Gulf
States a taste of winter, but rarely more than a few flakes.
It really all depends on the influx of air, its rate and direction. It
rains in Alaska and snows in Georgia on the same day merely because at one
place the air is coming off the Pacific, and at the other it is flowing
from the center of a refrigerated continent.
And the progress of these storms is one of Nature's greatest poems if you
take a minute to think of them sweeping on in majesty, the one thing that
man cannot control. Even the snow which is the citizens' curse as well as
the farmers' blessing becomes epic when it beleaguers an empire for half a
year.
DEW AND FROST
The very process that made the tumbler of ice-water sweat on the hot day
causes dew. And the formation of frost is analogous to that of snow. Frost
is not frozen dew, but the formation of moisture crystals at the
temperature of 32 deg. or below. Frost or dew form only on still,
cloudless nights. Even if no clouds are visible, neither will form if a
stratum of humid air has prevented radiation. Hence either dew or frost
is a fairly good sign of clear weather.
Three white frosts on successive mornings are followed by a rain. This
saying holds water not because there is any virtue in frost to cause rain,
but because a storm is normally due once a week. The frosts did not form
when the anticyclonic winds were blowing and usually not more than three
mornings elapse between the time that the anticyclone has lost its
influence and the time for the next cyclone to appear. Frost indicates a
considerable amount of moisture in the atmosphere, also, which tends to
increase as the cyclone approaches.
The heaviest dews come in late summer and the heaviest frosts in
mid-autumn because the change in temperature is greatest then and there is
a greater chance that there will be a calm at sunrise. The greatest frost
damage occurs in the spring because the tenderer crops are growing then.
Summer frosts used to occur in the northern parts of Minnesota and along
the southern boundaries of the inland Canadian provinces before the
forests were cleared off. The march of civilization has actually pushed
back the frost line some distance.
Frost may occur when the amount of humidity in the air is low and the
barometer rising at any temperature under 50 degrees at nightfall, the
clear skies permitting radiation enough under those circumstances to
produce the necessary cooling. An evening temperature of 40 degrees with
the clear skies and faint west breeze will almost surely produce a frost,
provided the wind drops. In such circumstances the only hope for the
farmer is that there is enough humidity in the air to cause a fog before
the frost-point is reached. A temperature touching 34 degrees would not
bring frost, however, if the sky was at all overcast. Frost is difficult
to predict because a night shift in the wind, cloudiness that forms after
midnight, or even a wind arising before the coolest period at dawn will
prevent its formation. On the other hand, clouds may disperse, the wind
may fall or radiation may be so rapid before sunrise as to cause a killing
frost unawares. The farmer who lives in areas disputed by winter and
spring may never be quite sure, but precautions should be taken on the
still, clear, dry nights with the thermometer at fifty or below.
Fruit-growers resort to fires or to coverings to protect their crops. The
fires are particularly worth while, not so much for their heat which at
best cannot be expected to warm up the great outdoors much, but for the
smoke which prevents radiation. A line of smudges such as campers use to
ward off the mosquito would spread a pall of smoke over an orchard
efficaciously. A snowstorm, the soft fluffy sort that falls in April or
May, can do much less damage to vegetation than a severe frost.
Temperatures are much lower on the ground than even six feet above the
grass. Naturally these temperatures are those that really influence most
vegetation and in England temperatures on the grass are given in the
weather report with the ordinary observations, being as much as six or
eight degrees lower on clear nights.
In some of the hot, dry countries, such as Arabia and Egypt, most of the
moisture that they receive falls in the form of dew. Falls, of course, is
a loose expression as the dew forms and does not fall, being different
from the minute particles of fog. The fog particles in suspension in the
air are estimated to be as small as 1-180th of an inch. When they grow to
1-80th of an inch in diameter they commence to fall. Fogs are chiefly
caused by the soil being warmer than the air above it; the vapor on rising
condenses and becomes visible. In the spring and fall currents of air blow
over rivers at different temperatures and the result is a fog. One does
not have a fog in the desert.
There are places in the ocean with cold and warm currents with the air
above them correspondingly different where fog is of almost constant
occurrence. The Gulf Stream off the Grand Banks of Newfoundland has a
temperature of 78 degrees, while the water on the Banks is 45 degrees so
that fogless days are rare along the line of meeting.
Frost is known in every part of our country, many localities in the
plateau section being exposed to it every month of the year. The thin air
and cloudless skies of the altitudes make radiation very easy and the
daily variation of temperature is much wider than along the humid coasts.
Those who have never looked into frost conditions throughout our country
will be surprised to read the warnings of the Weather Bureau.
From the station at Pensacola, Florida (frost-proof Florida!), comes this
statement: "Vegetables are subject to damage by frost during all seasons
of the year."
Pittsburgh, Pennsylvania, "Frost is likely to damage fruit or other crops
in May and September."
Phoenix, Arizona, "Frost is likely to do damage in December, February, and
March."
Baker City, Oregon, "Fruit and other crops are most liable to damage by
frost in April, May, June, September, and October."
Kalispell, Montana, "Frost damage for fruit, May 15th to July 10th; for
grain, June 25th to August 1st."
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 passage 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 surpasses 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 passing 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
cumulus 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 pass a
given point, but the period of rainfall, in which the winter storm's
amount is often surpassed, 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 passed 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
circumstances 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 cumulus 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 altitudes 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 pass 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.
Altitudes 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 passage of an energetic cyclone. Often when the wind,
having been in the southeast for most of the storm, is passing 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.
[Illustration: 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 reassuring. 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 quantities.]
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 space 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 passes 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 passes 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
principal 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 passes 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 shores 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
passes 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 class, 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 Canal the warnings will assume an even greater importance.
The best description of a hurricane that it has been my fortune to read is
in a story entitled "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 accumulated that it has to let go all at once and the
accumulation 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 passing 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 cocoon 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 passing 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 cumulus 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 classed 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 grass, 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 altitudes 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 circumstance 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
scrap 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 compass in their bones and joints."