Ask A Scientist© Weather Archive

name         yoram
status       student
age          30s

Question -   Is it normal that there are jet streams at 12,000 feet (4Km) 
that are 120 knots?

Dear Yoram-

   120 Kt winds at 12,000 feet are rare, but not unheard of. An unusually
strong mid-level pressure system might produce such winds over a small
region. But the upper-level jet stream, usually found above 18,000 feet can
reach speeds above 100 mph regularly, and at altitudes of 30,000 feet, 200
mph wind velocities occasionally occur. The "average" jet stream windspeed
in wintertime over the northern hemisphere is probably 110-140 kts, at
altitudes of 20 to 40 thousand feet.

Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO.
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Yoram,

The polarfront jetstream can certainly be as low as 5-6 km.  4 km would be 
exceptionally low, but it is certainly possible.  It is unlikely that the 
wind speed in such a jet would be as high as 120 knots,
but again, it is possible.

David R. Cook
Atmospheric Section
Environmental Research Division
Argonne National Laboratory
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