The National tribune. [volume] (Washington, D.C.) 1877-1917, 1891-06-04
THE WEATHER.
The Probability of Rain for any Locality.
ny LIEUT.. J. r. FINLEY, U. $. SIGNAL SERVICE


Correspondence invited. suggestions desired
and information cheerfuliy furnished. Every ef.
oTt employed 20 make this Bureau OF practical use
to the readers of THE NATIONAL TRIEUSE. All
communications should be adiressed-Wsdhsr,
THE NATIONAL TRIBUNE Office Washington, ID. CT
A study Of the distribution Of rainfall over
any region like the United States involves a
vast amount Of labor and the necessity for
long series Of authentic and carefully recorded
observations. lt is not with rainfall as with
temperature or pressure, where corrections of
more or less exactitude can be applied 10 reduce
readings to their equivalents at sea level. The
distribution, in vertical hight, Of the amount
Of rain varies in different ATTITUDES, and with
differences in the position Of the mountain
chains with regard TO the prevailing wind go
that two stations situated close together may
differ widely in the amount and in the seasonal
distribution Of their rain.
The frequency aud average daily amount Of
rain are quito important climatic Characters
tics, since in some localities the rain falls in
frequently and in heavy showers, while at
other places precipitation occurs often and in
moderate amounts. For example, the average
amount of rainfall on each rainy day is OBS
inch at Milwaukee, Wis; OBI inch ut ROches-
ter, n. Y; 0.19 inch Mt Pensacola, Fla, and
Oh inch at Poplar River. Mont.
If we divide the number Of days in n month
on which n measurable quantity OF rain mot less
than O.OI inch has been recorded by the total
number Of days in the month we get quotieut
which represents the mean probability that
rain will fall on any day in that month. De-
termined as above the probability Of rainy days
at Tatoosh Island, Wash, varies from a mini
mum Of 10 per cent. ia August 20 maximum
of so per cent. in December; at Erie, Pa, from
81 per cent. in August TO Sc per cent. in Decem-
Der; Chicago, from - per cent. in September
TO II per cent. in March; Boston the same as
,T.
sence of rain, in July and August TO 40 per
cent. in February; Jacksonville, Fla, from %
per cent. in April and December to 46 per cent.
in August and September; Yuma, Ariz., from
ono per cent. in May and June to eight per
cent. in August and February.
From the Missouri Valley eastward the nsIn-
Der Of rainy days during the year varies
generally, from 100 TO no. exceeding the latter
number only in the Lake Region especially
along the southern shores Of Lakes Erie and
Ontario, where they increase 10 III at Roches-
ter aud III at Eric. The largest number Of
days occurs on the southeast side OF the Lakes,
showing the influence Of the prevailing west
erly winds in bringing rain. North VOuey,
n. Y, with yearly average of 195, has prob
ably the largest number Of rainy days Of any
place in the eastern part Of the United States.
There are but 13i rainy days at Milwaukee
against l52 at Grand Haven, 13G ut Toledo, and
l6g at Buffalo. The number of rainy days in
creases steadily from the Missouri and Missi5-
sippi Valleys and the Gulf and Atlantic Coasts
toward Lake Erie. Over the Rocky Mountains
and the plateau regions the number Of such
days ranges, generally, from 20 20 90. On the
Pacific Coast it rapidly increases nOrthward
from ~ at San Diego to GG at san Francisco,
156 at Tatoosh Island, 22i at Stka, and the ex-
traordinary number of go at Unalaska, in the
Aleutan Islands.
The lower drainage basin Of the Colorado
River. the southeastern portions Of California,
aud the southern part Of Nevada show . re-
markably small number Of rainy days, there
being but y at Keller, Cal, and - at Yuma,
ATiZ.