The morning news. [volume] (Savannah, Ga.) 1887-1900, 1891-12-14
III wEArHERIN DOTS ANDLINEs
What the Weather Chart Means and
How TO Read It

| now TO hcd1 II
The weather service, siuce the signal bu-
resu wns Transferred 70 the agricultural de-
psr.meut, has undergone many chang s.
One OF toe improvements is in the weather
chart which is post,i daily at the MORN
ING News building and at the exchanges
aud various pu bic places in the city. Copies
are also sent out by he lJcal wea her bureau
I thr ugh Observer SmyLh in charge. Tue
chart Of the MORNING NEWS is daily
( scan ed by hu reds Of people. Tho chart
/ p esent an outline of the United States and
Canada, upon which Are shown the stations
/ where weather observations are taken daily
at O'Clock a. M. and O'Clock p. N. and tele-
graphed t. the principal cities.
These Observations consist Of readings of
the barometer. Thermometer, direction and
velocity Of wind, state Of sky whether
| cloudles5 or otaer wise, and amount of rain
| AID snowfall These are entered In symbols
and figures upon the map. Lines, called
isobars, are drawn through or near stations
where barometer readings are the same.
A separate one is drawn for each difference
Of one-tenth of an inch in the hight of the
bar meter. Dotted lines, called isotherms,
connecting places Of the same temperature,
are drawn for each 100 reading Of the
| Thermometer
The direction of the wind at each station
/ ia indicated by arrows, the arrows pointing
In the direction the winds are blowing. or
opposite TO the way vane points. The
general movement Of storm, in the United
States Is from west to east, and we may
liken them to q series of rather rounded at
mospheric waves OF which the crests are
marSsd high" and oval troughs or de-
pressions bet Seen are marked and called
low" These alternating highs and lows,
several hu bred miles apart, have an aver
age easterly movement Of about GOO miles
per day.
High winds and rain, and, If cold enough,
snow, usually precede the low area, o te
extending to q distance Of 600 miles; in ad-
vance Of the low center the winds are
generally southerly, and in consequence
bring high Temperature. When the center
of the low passes TO the east of q place the
wind at oncs shifts to the north, which
brings lower temperature and clearing skies,
d in winter cold waves or northers. The
temperature on a given parallel west of the
low may be reasonably looksd for on the
same parallel to the east when the low has
passed, a d frost will occur along and north
OF isothsrm of about 400 il the night is
clear and there be but little wind. FIJI
ing the low comes an area of high, bringing
sunshiny weather which, in its turn, is fol-
lowed by another low.
By bearing in mind few general rules as
to the direction and rate Of moveme It of
the low and high, with the blowing OF the
wind from the high toward the low, coming
weather changes may be foreseen by a
glance at the map. The centers of low do
not move across isotherms, bat follow their
general direction. The cloud aud rain area
In front of low IS about the size of the
latter aud oval, with the west side touching
the center of the low in advance Of which It
pr0gresses
When the tsotherms run nearly east and
west no decided change In temperature
will occur. Ii the isotherms directly west
of place incline from north west to south
east, it Will be warms IL from northeast
TO southwest it will be colder. Southerly
winds prevail west OF nearly north and
south line. cutting the middle Of high,
also east of like line cutting the middle of
low. NortherlY winds occur west of a
nearly north and south line passing through,
the middle of low, and aIEo east OF a
similar one through the middle Of a high.
An absence OF decided waves Of high or
troughs OF low pressure indicates a con-
tinuance OF existing weather, which will
last till later maps show q change, usually
first appearing Ia the west