Evening star., 1936-07-10
Cool Air
Continued From First Page.)

Continued From First Page.)
a great. wide. deep mass of heavy air
| flowing almost continuously from the
Atlantic over the Gulf OF Mexico and
parts of Mexico, turning northward
over New Mexico, Arizona and Central
California, and then eastward over the
mountain States and the grain belt.
Some of it may originally have swept
around from the Arctic. A good deal
| of it actually has passed over parts
of equatorial Africa before turning
westward across the Atlantic.
1t is heated when passing across
the tropical seas and the gulf. 1t
gets hotter and hotter as it passes
over hot arid Northern Mexico and
the Southwestern Desert. It is q
vicious circle. The longer the tropical
air stream travels unobstructed over
land the hotter it gets. That Is
how temperatures in Northern Mon
tana may be higher than on the Mex
lcan border. If there was an unob-
! structed flow Of this clock-wise cir
cling tropical air current 1t would be
hot in the Western and Central United
States all the time. and 1t would get
hotter as the Summer progressed.
Here is where the broken of chunks
Of the North Pacific high enter the
picture They flow over the Cascades
and over the Rockies. The tropical
air, on the northward turn of its
clockwise path. bumps into one Of
them. The only way 1t can get by is
to climb over. 1t has to 60 up or 3
miles, where 1t Ia cooled The mois-
ture Is squeezed out Of it and comes
down as rain. The lower air is cooled
The coolness extends far over the
Central States. This is the procedure.
| generally speaking. by which the
great plains and corn belt States get
their rain. 1t shows conclusively,
Weather Bureau experts say. how lit
tie the actual moisture in the soil Of
any particular locality has to do with
/ its precipitation. aside from local
! showers. When the Midwest gets
rain, it is likely. the water will have
come originally from the Atlantic
Ocean or the Gulf Of Mexico.
Not Breaking OF.
Now this Summer-and also in 1880
and 1934-the eastward floating
chunks haven't been breaking OF the
North Pacific high. There has been
big low-pressure area wedged be-
tween it and the North Pacific coast.
holding it together and pushing 1t
southwark. The North Pacific highs
have been coming over only at the
| rate of two or three a month when
there should have been five or six.
1t is matter Of interest that the
average Summer temperature Of West
ern Arizona is about 100. It doesn' t
vary much from day to day. The
country stays baked all Summer long,
even when much cooler weather is en-
joyed a few hundred miles or so to the
northward. This is simply because
the northward flowing hot air, fur
ther heated above the oven of
Northern Mexico. always passes across
Western Arizona without humping
into any of the cooler chunks of air
from the North Pacific. Hence this
part OF the country Is always dry and
hot in Summer. 1t would be the same
throughout the whole West II, q little
Farther North. the cold air masses did
not normally enter the picture.
| The above is an outline of the funda-
mental situation, but considerably
simplified. All sorts of complicatine
factors are entering the picture from
times to time-notably weaker masses
OF cold, wet air coming down east Of
the Rockies from the Arctic. At FIRST
the East did not feel the effects Of the
Western heat wave because there was
a cold air flow over Hudson Bay com.
ing down over the st. Lawrence
Valley and the Eastern Great Lakes
region. 1t was holding back the east.
ward now Of the hot air over the West.
ern mountains and plains. Thursday
this had practically disappeared
There was nothing in the way any
more. The hot air, some Of which may
originally have started over tn.
Jungles Of Nigeria or the Sahara
Desert, came pouring across the Ap.
palachians, all the time getting hotter
AS a result the Atlantic seaboaro
sweltered.
Shorter in the East.
Heat waves don't last so long in the
East, however. There Is always the
complicating factor Of masses of cold
air coming down from the North At.
lantic or Hudson Bay to break up thu
uninterrupted, clockwise now OF the
tropical maritime air and bring rair
and cool weather. The West has only
the broken of chunks of the NORTH
Pacific high to rely upon, with tn.
occasional masses of cooler air com.
Ing down over Western Canada.
The behavior of this North Pacific
high is tantalizing to Government
meteorologists. II its behavior coulc
be predicted, the problem of weather
forecasts for the great grain belt ol
the United States would be greatly
Simplified.