Evening star., 1941-03-09
Three KiIometer
Predictions Get
Jump on Weather
Radio Robots Scoring
From Is Stotions
Simplify Forecasts
By THOMAS r. HENRY.

BY THOMAS r. HENRY.
Weather forecasters here are get
ting a one or two day jump on the
weather by means of daily "3-kilo-
meter predictions"
Still in highly experimental
state, these are the newest tools of
meteorology.
The expected movement of cold
and warm air masses at the level,
about 212 miles above the earth's
surface, where alto stratus clouds
begin to form, is anticipated. The
interactions of these air masses have
a direct but complex effect on the
surface weather below them.
Hitherto the mere observation of
them has proved a great aid in fore
casting. BY calculating they will be
several days ahead of time, the fore
caster is that much ahead of the
game, says Charles L. Mitchell of the
Weather Bureau staff, who is max
ing tests of the new system.
Predicted Inauguration Day.
1t received its first tryout five days
before Inauguration day in January
This day always has been a bugbear
with the Weather Bureau. 1t comes
at the most uncertain period of the
year, when any prediction is most
likely to be upset. With his 3-kilo-
meter forecast before him, Mr.
Mitchell took a long chance and on
January IS predicted fair and cold
weather for January 20.
The next day if looked as if he had
blundered. A mass of warmer air
was moving up the Atlantic Coast
and all the indications from surface
observations were that there would
be either a cold rain or snow. At
any other time the forecast would
have been changed. Mr.. Mitchell
studied his 3-kilometer maps and
stuck to his guns. Regardless of
what appeared on the surface of
the earth, he said, 1t could be seen
that the oncoming warm air mass
would turn out to sea somewhere in
the neighborhood of Norfolk, leav-
ing Washington unaffected.
Simplifies Complex Method.
The forecasts, he points out, are
q great simplif1cation of the very
complex air mass analysis methods
now being introduced into meteor
ology and usually can be made in
about IS minutes. Then they serve
as a general guide in interpreting
surface weather indications where
there are so many details that the
forecaSter may miss the forest be-
cause of the trees"
Generally speaking, Mr. Mitchell
said, forecasts based on the 3-kilo-
meter predictions will not differ
much in their details from those
based on surface indications. The
advantage is that they can be made
more specifically and with much
more certainty-in line with the
Weather Bureau policy of ehmi-
mating the word probable" from
It's predictions.
The data from which the maps
are made up, Mr.. Mitchell said,
now are obtained almost entirely
from automatic observations made
by those wire-brained robots, the
radiosondes, which now are sent
up from 25 stations twice a day into
the stratosphere where there is
no further change of temperature
with altitude. The ideal toward
which forecasts are working is
rs such observations twice a day.
Find Coolest Spot.
The robots, carried aloft 10 or
Is miles in balloons and dropped
with red silk parachutes after they
reach a point where the balloons
burst, radio back to earth run
ming account of the temperatures
and pressures through which they
pass. Thus it is possible to con-
struct daily weather maps of the
stratosphere itself, but this is not
so important for practical purposes
as is the 3-kilometer level.
Among the recent observations of
the robots is that the coldest spot
over United States territory is about
~ dDONC oWdll 1SldIlu, III GIl6
Caribbean, where the thermometer
sinks regularly to go degrees below
zero. In the stratosphere over
Omaha, for instance, the tempera-
ture is only minus so.
The high atmosphere observations,
Mr.. Mitchell pointed out, may aid
greatly in interpreting the move
ments of air masses at the 3-kilo-
meter level. Weather maps of the
stratosphere now are being con-
structed at the Massachusetts Insti-
tute of Technology which cover the
entire North American continent
and extend far over the Pacific.
A method Is being worked out to
calculate stratosphere conditions
from surface reports received from
ships.