Evening star. [volume] (Washington, D.C.) 1854-1972, 1897-11-17
Bulletin Giving Interesting Informa-
ton Issued by Weather Bureau.
SPECIAL ATTENTION TO CROP SEASON
Rainfall in United States Every
Day in Year. a
so : CALLED CLOUD BURSTS

Henry, under the direction of Willis l..
Moore, chief of the weather bureau. The
bulletin is profusely illustrated, with an
nual. seasonal and other charts, and the
rainfall of the crop-grow.ng season has re-
ceived attention separately.
The bulletin, compiled from statistics ex-
tending over many years, states in the in
PRODUCTION that it is quite probable that
rain falls in the United States at one point
or another every dey of the year. On very
rare occasions the observers of the weather
bureau report no precipitation at given
hour, but it should be remembered that
their range of vision can cover at the ut
most less than ore-hundredth part of the
whole area.
The theories Of rainfall given in the books
of twenty or thirty years ago are not now
wholly accepted There is one very simple
principle, however, upon which no disagree
ment exists-that in order to produce album
dant rain the temperature of air must be
suddenly cooled below the dew-point
When the air IS thas cooled, a portion of
the water vapor which is always present
within it is charged to the liquid states. and
that which formerly existed as a gas or
vapor now becomes visible in the form
minute particles of fog or mist The par
ticles thus formed may float away with the
wind. or they may increase in size, cOalesce
ana fall to the ground of their own weight
Whether the condensation of vapor thus
Cultured results simply in cloud, or whether
rain falls. depends on the magnitude OF
the temperature changes that take place
in the air mass whose vapcr is being con-
deEsed. A rise in temperature is ninlical
to further condensation: fail is favorable
to precipita ton.
Matter of Doubt.
The precise manner in which air is cooled
sufficiently to produce rain. whether by
contact or by mixing, is not clearly appre-
herded. Cooling by expansion as air as
cends is one of the most effective causes OF
rainfall. The ascensional movement of air
is brought about in several ways, chief nf
which are: The air may be forced up the
side of a mountain into region of dim:n-
ished pressure and lower temperature. as
happens whenever mountain range runs
in a direction at right angles to the pre-
valllng winds; in the warm season, the
lower layers of the atmosphere under the
effect of solar radiation, and probably 9TH
er causes, frequently reach a state of UNI
stable equilibrium. thus inducing ascen-
sonal currents-summer thunder storms
are largely the result of this process: last.
and doubtless most important of all, is the
circulation of air in cyclonIc storms, VIZ. a
radial inflow from all sides and an ascen-
sional movement in the center. A very
large percentage of the rain of the United
States IS precipitated in connection with
the passage of storms of the latter class
The conditions which affect or control
the rainfall may be divided into two class
es, permanent and variable. The perma-
nent conditions which contribute to an
abundant rainfall chiefly nearness to
the ocean or other large body of water, a
location within or near the track of cy
clonic storms: mountain ranges, particu-
larly those running in a direction at right
angles to the direction of the rain-bearng
winds. These conditions may operate sin
ely or in combination.
rhjc
distribution of precipitation in the United
States are as follows: There is a narrow
belt of very heavy rainfall on the northwest
coast, extending from Cape F!attery on the
north to midway of the Oregon coast on
the south. and inland as far as the sum-
mits of the coast range, including in that
designation the main and collateral ranges
of mountains extending from southern
Oregon to the Straits of Fuca. Eastward
and southwark the annual fall diminishes,
reaching minimum on the lowlands and
valleys included between the coast range
on the west and the Sierra Nevada and
the Cascade ranges on the east. The pre-
cipitation increases from the valleys to
the mountain tops, thence falls away very
rapidly with descent on the eastward slope
until the great plateau is reached. Here
the fall ranges from ) to Is inches, with
isolated areas where it rises to 90 inches
and over. There is but little increase as
the western slope of the Rocky mountains
is reached, except in central and northern
Idaho.
ecSSitatiOn ON Mountain Slopes.
The precipitation On mountain slopes and
submits is known to be large, but guam
tirative statement of the annual depth
cannot yet be made. The rainfall of the
foothills region east of the Rocky noun
tains ranges from 10 to IS inches, and it
increases slowly toward the Tooth meridian
Eastward of that meridian the annual pre-
cipitation varies from little under 20
inches to about 60 inches on the Florida
and gulf coasts. There is gradual de-
cline both from the Atlantic coast west
ward and from the gulf coast northward.
The diminution in fall from New Orleans
northward to St. Paul is 81 inches: from
Eastport westward to ST. Paul. II inches.
The rainfall conditions of the Pacific
coast are quite different from those
of the east, as has been stated
Grain sown in the fall begins to
sprout with the first rain, and thenceforth
grows more or less slowly throughout the
winter. 1t is ready for the reaper from the
1st of June to the list of July, according to
latitude. and with the harvest comes the
end of the rains. Fall-sown grain in the
east makes little, If any. growth during the
winter, but with the advent of warm
weather in the spring the plant grows rap
idly under favorable conditions of heat and
moisture. April to August may therefore
be called the critical months for the staple
crops in the eastern two-thirds of the
United States, and 1t is with the rainfall Of
THESE ufOntNS tHdt the dSFlcuIturlSt Is cnfeI7
ly concerned. The tables below show the
normal rainfall of each month of the grow
ing season, including September, the total
for the season, the greatest and least sea-
sonal fall during the period of observation
and the ratio of the seasonal to the annual
fall.
The exact amount of rainfall required for
the successful cultivation of crops has not
been fixed nor can be in terms of rainfall
alone On the Pacific coast and over COM
paratively small areas in the arid regions
wheat and other cereals are grown with
seasonal rainfall considerably less than fif-
teen inches, but it should be remembered
that the climatic conditions, as regards
temperature and humidity, are quite differ
ent from those which obtain in the wheat
region of the northwest. The character
of the soil. especially as regards it's ability
to retain moisture, very important con-
sideration. 1t is said, in explanation of the
fact that wheat is grown in eastern WASH
ington, where the yearly fall is generally
under eighteen inches, that the rainfall of
winter and early spring is conserved in the
soil and is supplied ito the plant by capil-
larry action during the early part of the
growing season.
Rainfall Variability.
One phase of rainfall variability that may