The Cambria freeman. [volume] (Ebensburg, Pa.) 1867-1938, 1890-01-17
Explanation of weather Charts.

SIGNAL OFFICE. WAR DEPARTMENT,
WASHINGTON CITY.
The Signal Of1cer hiss decided to distrib-
ute as widely rs possible the daily weather
charts. In order that the intelligent part of
/ every community may utilize them by max
I ing special and local weather predictions,
and thus supplement- the official forecasts.
/ which, being for large areas OF country,
must necessarily be brief and very genera
! in their character. In order TO supplemer
! the knowledge of those who are unacquaint- T.
! ed with the general accepted meteorological
methods, q few words OF explanation are
considered advisable.
Storms are divided into two general
classes, one In which a deficiency OF pres
sure occurs, commonly known as Glow" and
another which appears In the form of an
area of excessive pressure, aud which Is
briefly knOws as "high."
In order to show clearly the atmospheric
pressure, the points having al equal pres-
sure are connected by lines called isobars.
which are drawn for every tenth OF an inch.
These isobArs show that the atmospheric
pressure over the earth alosg the line is
equal to thar which ~ould be exercised by
layer OF pure mercury OF a thickness cor
responding to the number OF inches marked
against ths Isobar.
Low areas travel across the United States
by diverse paths-the average direction be-
ing a little TO the north Of esst-with q We
Iocity OF about i've hundred miles each
tWeHty four hours. The winds blow con-
trary to she movement OF the hands OF q
watch. spiraliy inward towards tbs area of
lowest pressure. and their strength and vi
oIeuce are prOpornoned to the difference Of
pressure and temperature, which on these
maps are Indicated by the crowded condi-
tion OF isobars and isotberms. The low area
preceded by cloudy weather and rain, which
sometimes extend many hundred miles In
advance OF the center. 1t is also preceded
by temperature quite high for the season,
except IN very hot weather, when the tenn
perature. sltsongh higher by night. is lower
by day owing to cIoudiness. AS q general
rule essterly and seutherly winds are found
in front OF low areas. When the low area
passes place the winds shift into Dortherly
or westerly. rain soon ceases. and fair
weather shortly after follows.
high areas generally follow low areas.
About one-half of them move eastward
from Minnesota TO New Eog'and, affecting
the northern half Of the United States
the Others move 6rst southwark In the
trans Mississippi country to Texas, then
drift eastward with the general circulation
OF the air, thus affecting the whole country.
These high areas frequently advance with
sufficient fOrcs and psrsistsncy to cause
winter storms OF sevsTity and violence. The
circulation of the winds is reverse to that in
low areas. as the current b lows out spiraly
from tie center, in = direction correspond
ing to the movement OF the hands of q
watch With the sdvascing high areas the
temperature falls and the weather usually
clears, especially 10 summer, when the
"hIghs" srs rarely of sufficient force to
cause storms. When high area il moving
of the Atlantic coast with its center over
New England or the Saiut Lawrence Val
ley, Il frequently occurs that the northeast.
erly winds OF such area bring rain and
eIoudIness along the New England and
Middle Atlantic coasts In the winter time
the advance of high areas Is often marked
By very severe falls OF temperature, which
occa asionally amount 20 twenty-five or thirty
degrees in twenty hours. Whenever
the temperature falls more than fifteen de-
grees In twenty~fouT hours and sinks below
forty-aYs degrees. as happens at times with
high areas, IT Is called cold wave. The
paths of high areas are also easterly. In gon-
eral. A W. GREELY,
Chief Signal Oficer.