Yorkville enquirer. [volume] (Yorkville, S.C.) 1855-2006, 1914-05-08
atlisesllausaus &sading.
FoRETELLING THE WEATHER
Bureau Has to Proceed Along Purely
Scientific Lines.

made
To this the shortest and simplest
answer is: By telegraph. The wealth
er forecaster does not look out Of the
window and guess. He is not wealth
erwise like the old salt who scents
the approach Of a storm without
knowing how. To the signs by which
the ordinary citizen decides whether
to take his umbrella with him or
leave it at home he pays no attention.
Give him his telegraph wires and he
can make his predictions as accurate
| ly in a windowless cellar as on the
top of New York's highest skyscrap-
er.
The private individual sees the
clouds settle on a nearby mountain
or the rain sweep over a field mile
from his house and knows that the
storm will be on him in few min
utes. Wit. the aid Of the telegraph
the weather man sees the same storm
when it is a thousand miles away,
and not only this storm, but every
other in the country. He knows In
what direction and at what speed
each is moving, and can thus calcu-
late with reasonable accuracy the ap-
proximate time when it will reach any
place in its route.
Twice a day, at in the morning
and in the evening, reports are
telegraphed to Washington from
about 200 observers stationed in as
many different localities in the United
States and Canada. In these reports
the observers do not volunteer their
personal opinions about what is going
to happen. They confine themselves
to a plain statement of the actual
conditions at that particular mo-
ment, the pressure, or weight, OF the
atmosphere, the temperature, the di-
rection and velocity Of the wind, the
amount Of rain since the last report,
and so forth. From this information
the weather map of the United
States is made up, showing the con-
ditions that prevail in every part OF
the country. Since there are two
maps for each day it is obvious that
by comparing them the forecaster can
keep track Of the course and progress
of both storms and periods of clear
weather From that, the next step
is to predict what sort Of weather
will prevail for a day or two in any
given locality.
This map is the basis for all scien-
tific weather forecasting. A glance
at it will show that it Is divided into
high pressure areas" and "low pres
sure areas" These are technical
terms used to describe the regions in
which the weight or pressure of the
atmosphere is great (high) or small
Qow). At sea level the barometer
which is used to measure this weight,
will register 80 inches under normal
conditions Of the atmosphere. When
it registers more than this, say 3O.5
or 81, the pressure is "high;" when
29.5 or less, '1ow." In this way the
height Of a column Of mercury in a
barometer indicates the weight Of the
air just as, in a thermometer, it in
dicates the temperature.
Low pressures usually mean strong
winds, rain, and rising temperature;
high pressures, cool, clear weather.
For a reason to be explained later,
these "highs" and lows" as they
are called, travel in a general direc-
ton from west to east. The fore
caster notes their progress on the
map, preceives their speed and their
route, and then predicts the time of
their arrival at any specified point.
If they travelled, like a ship steered
by compass, an exact course to the
east, and if they moved invariably al
the same speed, then weather fore
casting would be a simple sum in
arithmetic, like calculating the time
when a railroad train running 5OI
miles an hour will arrive at station
500 miles away. But storms are not
railroad trains. They travel in an
easterly direction. but they do not
travel due east. Their speed is liable
to change, and they are affected by
the presence of other storms, by
mountain ranges, large bodies of
water, and many other things which
make weather prophesying the COM
plicated science that it is. The skele-
ton of the science, however, is the
progress of these "highs" and lows
eastward across the country.
This progress is caused by the
shape of the earth and the we'll
known fact that hot air rises. The
tropical sun in the regions along the
Equator heats great masses of air.
which rise and drift toward the North
and South Poles. AS the earth re-
wolves from west to east these masses
are carried along with it at the same
speed But, as is also we'll known
the Equator revolves much faster
than the poles, which are practically
stationary, in much the same way as
the rim of a wheel revolves faster
than the hub. Therefore these mass
es of air, revolving at the same rate
as the Equator, begin, as they ap-
proach the poles, to move much fast-
er than the earth beneath them There
is thus a constant movement of the
atmosphere from west to east,
movement which becomes more mark
ed the nearer one gets to the poles.
This, of course, does not mean that
the wind always blows from the west
The great current flows in that di-
rection, but surface conditions cause
innumerable eddies which are the
winds we feel. Into a low pressure
area, for instance, the air rushes
from every direction. Thus, II the
center of the disturbance is to be to
the west of us, we will have an east
erly wind as the air rushes toward
this center; when the storm has
reached and passed us on it's east
erly way we will have westerly
winds. For this reason it is common
to say that west winds mean clear
weather.
The air that flows into the low