R
EVISION
:
-
D
ATE
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12/29/04
P
AGE
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14
Copyright
2004 Glasair Aviation, LLC Arlington, Washington All rights reserved
Mountain Flying
Pilots flying in mountainous areas should inform themselves of all
aspects of mountain flying, including the effects of topographic features
on weather conditions. Many good articles have been published and a
synopsis of mountain flying operations is included in the FAA Airman’s
Information Manual, Part One.
Avoid flight at low altitude over mountainous terrain, particularly near
the lee slopes. If the wind velocity near the level of the ridge is in
excess of 25 knots and approximately perpendicular to the ridge,
mountain wave conditions are likely over and near the lee slopes. If the
wind velocity at the level of the ridge exceeds 50 knots, a strong
mountain wave is probable with extreme up and down drafts and
severe turbulence.
Standing lenticular clouds are visible signs that a mountain wave exists,
but their presence is dependent on moisture. Mountain wave
turbulence can, of course, occur in dry air and the absence of lenticular
clouds should not be taken as any assurance that mountain wave
turbulence will not be encountered.
The worst turbulence will be encountered in and below the rotor zone,
which is usually 8 to 10 miles downwind from the ridge. This zone is
sometimes characterized by the presence of “roll clouds,” but only if
sufficient moisture is present.
A mountain wave downdraft may exceed the climb capability of your
airplane. Avoid mountain wave downdrafts.