Reading the WeatherLongstreth, T. Morris (Thomas Morris)
Science
Reading the Weather
Longstreth, T. Morris (Thomas Morris)
Weather forecasting
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.
Public-domain text, read in full here on John Shaqi.
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