The National tribune. [volume] (Washington, D.C.) 1877-1917, 1890-05-29
THE WEATHER.
Mountain and Valley Winds.
BY LIEUT.. }, p FINLEY, U. $. SIGNAL SERVICE.


correspondence invited. suggestions desired
and information ohesrfuy furnished Every ef-
Tort employed To make this Bureau OF practical use
To tae readers Of fnE NATIONAL tribune. All
communications should he addressed Weather
IHE NATIONAL TRIBUNE Office. Washington, d. q. I
On the slopes of mountain ranges aud tho
plains near the base, and especially in deep
valleys extending from the slopes into tho
country below. there ARE often strong winds
toward aud up the mountain-side during tho
day, and the reverse at night. This fact is we'll
known 10 hunters aud all who are accustomed
To encamp in the mountains at night and so
tho camphres are always placed below the
tents Cd the slope, that the smoke may be
drawn away by the descending current, instead
OF being blown toward them. Such currents of
course extend TO some distance over the plain
below, and where the air Is brought together
by a number Of rAvines aud deep valleys into
one common aud somewhat contracted current
below the force Of the wind may be very great
Just the reverse takes place during the day.
for the air then rushe5 up tho mountain.side
from the plain below, and If this air is concon =
trated into narrow valleys, either near the
base OF tho mountain or up the side the cur
rent becomes unusually strong.
The winds in the mountains Of the ii imalayas
blow up the valley during the day from o a. H.
TO p. M. and down during the corresponding
hours of tho night. AT the debouches of the
principal streams into the plains these night
winds blow with great violence, particularly in
the Winter. They diminish in force as we as
cend the mountains, aud at great elevations
aud in the plains of Western Thibet the nights
are almost perfectly calm. The diurnal winds.
on the other hand, in the latter country are
terrific, aud in travelling there they are antici-
pated with real dread
Among the mountain-peaks Of Colorado
strong currents arc observed rushing directly
up the sides, while on the erests which may be
only few rods in width, nearly perfect cal M
prevails. This calm is produced by tho as
eonding currents on all sides of the peak, con-
tinuing upward, after leaving the edge of the
crest, in prolongatlon of the direction of the
sides, and meeting at common center some
distance above tho crest These conditions pre-
vail about midday, but iate in the afternoon
slope being cooled down to about the mean
temperature of the day. During the night,
especially in the latter part of it, there is a
reverse current down the mountain of about
the same strength as the midday one, and con-
These winds depend upon the Same circum-
stances and are explained upon precisely the
| same principles rs the land and sea-breezes on
| monntain-slopes along sea coasts; in fact the
only difference Is in the circumstance that In
the one case there is water, and in the other
plain at the base of the slope.
A similar but much feebler effect Is observed
| on long declivites of open country with only "a
| very small gradient, such as that between the
| Mississippi Valley and the Rocky Mountains
| but in such cases it is generally somewhat
masked by other prevailing currents. SO that