The record-union., 1891-03-22
WEATHER FORECASTS.
Lieutenant Finley Tells Why and How
They Are Made.
Summer Weather More Difficult to
Deal With Than Wfnter-Some-
thing About Storm Centers.

Lieutenant Finley of the Signal Service
has just issued the fifth of his interesting
and instructive letters descriptive of the
workings of his department. This latest
letter gives some very interesting facts
| about weather forecasts.
The branch Office of the National
Weather Service, Division of the Pacific,
says the Lieutenant, was opened at San
Francisco March l, 1885, and is the only
| office of its kind in the country outside of
the central office at Washington, d. c..
1t was established for the purpose of
providing, in the most direct and practi-
cal manner, an opportunity for the peo-
pie OF the Pacific coast to receive all of
the benefits that may be derived from
the work of the Signal Service The
main object was to prepare and distribute,
through the press and by telegraph,
weather forecasts for the Pacific Coast
States, and warn vessels of the approach
OF storms dangerous to shipping off the
coast; also, to make special forecasts of
ram, frosts, floods and local storms.
such work had been carried on at the
central office in Washington many years
IOr the eastern portion of the United
States, and 1t was believed that the time
1.'NN COiiO All liic OF IL L
Coast weather service, with headquarters
at the metropolis of the coast, and at a
place centrally located for the convenient
receipt and distribution of telegraphic re-
ports. To properly
APPLY THE WEATHER FORECASTS
To definite areas of country, the Pacific
Coast was divided into three districts,
designated officially as follows: North
Pacific Region embracing Western Ore
OOn and WaStnrp
Pacific Region embracing the western
portion Of California north of parallel 81
degrees north, or an east and west line
cutting the northern edge of the bay of
Monterrey, South Pacific Region (em-
Draclng the western portion of California
south of parallel 81 degrees north. On
May L, 1886, an order was issued from
washington changing the districts to State
areas, and thereafter the weather fore
casts were made for the following regions:
washington (embracing the entire State),
oregon embracing the entire State).
Northern California embracing that
portion OF the State north of the latitude
OF 80, or an east and west line passing
through the central portion of Lake
Iulare). Southern California embracing
that portion of the State south of the lati-
tude of 360). There have been several
changes in the hours at which the fore
casts have been prepared for issue. de-
pendent upon the hours of
METEOROLOGICAL OBSERVATION
And the convenience of the press. OBJ
servations are now taken throughout the
United States at S A. NJ. and at P. NJ. 18th
meridian time, which corresponds to A.
NJ. and p. NJ. Pacific time. The weather
forecasts are issued from the San Fran
cisco Office about $50 A. NJ. and $3.50 p. NJ.
daily. An earlier hour cannot be selected
because OF the want of telegraphic faciIi-
ties in concentrating the reports at San
Francisco from all parts of the Pacific
Coast States. The language of the fore
casts must largely conform to the official
instructions issued from the central office
at Washington.
Forecasts of higher or lower tempera
ture are made each morning with refer
ence to the expected minimum tempera-
lure OF the following morning, and each
evening with reference to the maximum
temperature expected on the following
afternoon. The forecasts of stationary
temperature indicate change of four de-
grees or less from March to October. in
elusive, and six degrees or less for the re-
naming months Of the year. In the case
OF higher or lower temperature change
OF one degree or more is sufficient to YER
lfy the forecast. A cold wave in general
terms, is defined to be a fall in tempera-
ture over an extensive area of 200 in "a
hours, or 2S' in 48 hours, and to
THE FREEZING POINT
Or below. Warnings of cold waves are
issued when it is expected that the area
affected will exceed 100000 square miles
in extent, and in well defined cases for a
lesser area. Forecasts of fair weather
mean an entire absence of rainfall. but
not necessarily an absence of clouds.
Forecasts are usually made for a period
of "A hours, but whenever the meteor
illogical conditions are so decided as to
dominate the present and are expected to
materially modify coming weather over
any extensive part of the country, fore
casts may be made for periods of sc, As
and u hours.
Generally speaking, it is more difficult
to forecast accurately the weather of sum-
mer than that of winter, because of the
absence i'll the former season of well-de-
fined storm centers, most of the precipita-
ton being the result of local changes in
temperature and wind direction. For
similar reason it is more difficult to fore
cast the changes of a moderate storm than
of those which attend severe one. be-
cause in the latter case the laws of cv-
clonic development and progression are
more closely adhered to, which permits
the principle of weather forecasting to be
applied with greater success.