Evening star., 1939-04-26
lowering Air Giant
Found 10 Repu|se
frieid Assaults
Dr.. WexIer Tells Of
Odd Condition in
Rocky Mountain Area

Odd Condition IN
Rocky Mountain Area
A 15-mile- high mass of warm,
heavy air with Its cold feet planted
in the Great Basin just west Of the
Rocky Mountains like a titan body
guard of half a continent, catches
and tosses winter storms out of the
United States into Canada and is
one of the determining factors of
American weather.
This is the Great Basin high. de-
scribed by DR.. H. L. Wexler of the
United States Weather Bureau be-
fore the American Meteorological
Society meeting here today. Storm
bringing lows" careening across the
mountains from their nests in the
Pacific, bump into this meteorologi-
cal giant and can advance no further
into the interior of the United
States. The Canadian northwest
gets the benefit of them.
The trouble is, DR.. Wexler ex-
planned. that the bodyguard will not
stay on the job It is only semi
permanent, sometimes persisting for
month and sometimes only for a
week or two. Every now and then
the storms find the door to the
Great Plains wide open and rush in
to wreak havoc.
Changes Direction.
The Great Basin high was de-
scribed by DR.. Wexler as a dynamic
anticyclone." The most common
type of high, he said, is shallow and
fast moving. The mass of cold,
dense air moving in a clockwise di-
rection is only few miles thick next
to the surface of the earth. Above
that it's motion becomes anti
clockwise and the pressure decreases.
Such highs are Matched in the
Arctic and are frequent visitors in
winter, sweeping down the valley of
the Mackenzie River or across the
Great Lakes from Hudson Bay with
express train speed and turning
eastward with cold and storms across
the United States.
The other type, he explained, is
composed of warm, heavy air. It's
true nature has only become known
with upper air observations which
show that it remains practically un-
changed up to great heights. The
mos notable of these is a superpiant
which uses the island of Bermuda as
a footstool and sprawls eastward
and westward across the Atlantic
Storms occur where other air masses
bump into it. In 1887 it took a stem
westward and rested one foot on the
Southern Appalachians. The great
Ohio Valley floods were the result.
This Bermuda high influences pro-
foundly the weather of the East and
Midwest.
Creates Heavy Fogs.
The Great Basin high DR.. Wexler
explained, is similar in structure but
not quite SO permanent. 1t consists
OF a pancake of dense. cold air
pushed down by a great mass of
heavy. warm air. When it is on
the Job fog is SO heavy airplanes
cannot land. The strange condition
is seen where the foothills and sum-
mlts OF mountains are covered with
snow While the slopes themselves
are having spring thaws. Some
times the air titan sprawls far to
the northward. Winds of from 60
TO 80 miles an hour sweep down the
Columbia Valley as the cold air tries
TO escape the crushing weight
above it.
This is one of the five or six
weather cells" in the northern hem
lsphere, DR.. Wexler explained
Others include the Bermuda high,
one over the Middle Pacific and an
other sprawled over Siberia. with
permanent lows in the Pacific north
OF Hawaii and in the North Atlantic
around Iceland. Whatever happens
In these cells has profound effects
on the weather of the hemisphere.
The most probable explanation of
them, DR.. Wexler said, is that the
prevailing westerly winds of the
northern hemisphere. due to the
combined motions of the earth and
the temperature gradient from north
to south, throw off eddies as they
speed around the world. To the
north they throw anti-clockwise
moving eddies and to the south
clockwise moving ones.
Trapped by Surface.
Ordinarily, he said, such an eddy
would simply whirl around. brush
the land or sea. and come back into
the parent winds again. But in
some places the geographical fea-
lures are such they get trapped and
pile up into the permanent highs
and lows which determine the
weather of the world. Conditions
over the seas are so little known
and upper air soundings so recent.
he explained, that it is not possible
to tell how they become trapped.
The Great Basin high is the most
notable Of those found on the land
and can be explained because the
region is natural cold air trap.
When a heavy layer of cold air is
piled up there it prevents the eddies
thrown off by the winds from making
the complete circuit and they con-
tinue to pile on top of each other.
Occasionally. he pointed out. SINH
lar highs start building up in the
East. Arctic highs sweeping in over
the Great Lakes get trapped and
stay in one position, becoming taller
and taller all the time, for week
or more. But the geographical fea-
lures of the land are not such that
they can hold their positions for a
much longer period.
Congress in Brief