River Falls journal. [volume] (River Falls, Pierce County, Wis.) 1872-2019, 1914-05-07
HOW THEY FORECAST THE
WEATHER

Will you please tell me through
the News paper, in simple langu-
age how the weather forecasts are
made?
To this the shortest and simplest
answer is: By telegraph. The
weather ~forecaster does not look
out of the window and guess. He
is not Weatherwise 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
accurately in a WindoWless cellar
as on the top of New York's high
est skyscrapper.
The private Individual sees the
clouds settle on a nearby mount
ain or the rain sweep over a field
a mile from his house and knows
that the storm will be on
him in a few minutes. With
the aid of the telegraph the wealth
er man sees the same storm when
it is a thousand miles away, and
not only this storm but every one
in the country. He knows in what
direction and at what speed each
is moving, and can thus calculate
with reasonable accuracy the ap-
proximate time when it will reach
any place in it's route.
Twice a day, at s in the morning
and at 8 the evening, reports are
t~elegraphed 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 p~ersoal opinion
about what is going to happen.
They confine themselves to a plain
statement Of the actual conditions
at that particular moment, the
pressure, OF weight of the atmos-
phere, the temperature the direct
ion and velocity Of the wind, the
amount of rain since the last re
port, and SO forth. From this in
formation the Weather Map of the
United States is made up, showing
the conditions that prevail in eV-
cry part of the country. Since
there r 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 wealth
er. 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
scientific weather forecasting.
A glance at it will show that it is
divided into "high pressure areas
and slow pressure areas" These
are technical terms used to des-
cribe the regions in which the
weight or pressure of the atmos-
phere is great (high) or small dow
At sea level the barometer, which
is used to measure this weight,
will register 80 inches under nor
NAL conditions of the atmosphere.
When it registers more than this,
say 3O.5 or 81, the pressure is 'high'
when 1915 o. less, "low." In this
way the height of a column of
mercury in a barometer indicate
the weight of the air just as, in a
thermometer, it indicates the
temperature.
Low p%ressures 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 direction from west
to east. The forecaster notes their
progress on the map, perceives
their speed and their route, and
then predicts the time of their ar
ival at any specified point. If
they travelled. like a ship steered
by compass, an exact course to
the east, and if they moved in
variably at the same speed, then
weather >fo~recasting would be a
simple sum in arithmetic, like cal
%culating the time when a railroad
train running so miles an hour
will arrive at a station 500 miles
away But the storms are D Il
railroad trains. They travel in an
easterly direction, but they do not
travel due east. Their speed is
liable to change, and they are af-
ected by the presence of other
storms, by mountain ranges, large
bodies of Wafap and poonu afhor