Instrument Flying: Technique in Weather Page: 52
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RESTRICTED
T. O. No. 30-100D-1for some distance behind the front, followed by a
broken or overcast sky with low clouds, will indicate
such a development. Squalls in the forward portion
of the following cloud area are an almost certain
indication.
3. What is the stability of cold air? Stable air
produces stratiform clouds, unstable air produces
cumuliform clouds.
4. What is the altitude of the freezing level? Ask
the forecaster, or refer to upper air observations
or pilot reports.
5. What is the stability of warm air? Stable air
will produce stratiform clouds - if sufficient moisture
is present, nimbostratus. Unstable air will producecumuliform clouds - if sufficient moisture is present,
cumulonimbus.
6. Are there indications that a prefrontal squall
line will develop? Refer to the section on prefrontal
thunderstorms in section VII.
7. If flight through the front must be made, where
will the front be met? Will you change altitude on
passing from one air mass into the other? Will you
fly contact, on instruments, or over the top?
A cold front may possess any degree of intensity.
An experienced pilot will encounter various degrees,
but one thing is certain. If he has ever crossed a
severe front, he will be on his guard. He will, in
every case, carefully study the factors listed above
and will proceed with caution.The type of weather associated with both warm
fronts and cold fronts is governed by the same factors;
that is, the stability and vertical motion of the two air
masses involved. Therefore, the paths to be followed
when flying through a warm front can be tentatively
decided upon before take-off if the pilot follows the
same rules, and changes in flight plan will depend
upon the pilot's observation of actual conditions.
The vertical motion of the air masses is of two types;
both air masses ascending, or both descending. Al-
though descending air occasionally occurs along upper
warm fronts, it is rare at the surface. Therefore,
warm front activity of any consequence generally
results from ascending air in both air masses.
The activity along a typical warm front develops
from the lifting of the warmer air mass to its con-
densation level as it flows upward over the obstruct-
ing wedge of cold air. Eventually, as the upward
flow continues, the clouds thus formed pass the ice-
crystal level and precipitation occurs. The intensity
and extent of warm front activity will depend upon
the slope of the front, the stability of the air masses,
the height of the condensation, freezing and ice cry-stal-levels, and the speed with which
flows up the front.the warm air
CLOUD CHARACTERISTICS
Because warm air generally has a high moisture
content, the clouds first forming within it over the
front will be dense. The severity of icing conditions
and turbulence will be determined by the instability
of the warm air, and the location of icing regions by
the height of the freezing level. These two factors,
the stability of the warm air, and the height of the
freezing level, are important, especially if the front
has previously shown only limited activity. Absence
of activity does not necessarily mean that the warm
air is stable; it may be conditionally very unstable,
and ready to produce extensive thunderstorm activity
as soon as the lifting progresses far enough.
The cold air mass ahead of a warm front may
always be considered stable, since it is overrun by
warmer air. Even though its lapse rate indicates in-
stability, vertical motions will be limited and clouds
within the cold air will be of the stable type - stratus
and altostratus.RESTRICTED
Section 8
Section 94
WARM FRONTS
"I
I.
52
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Army Air Forces. Instrument Flying: Technique in Weather, book, January 1, 1944; Ashland, Ohio. (https://texashistory.unt.edu/ark:/67531/metapth873973/m1/58/?q=+date%3A1941-1945: accessed July 16, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu; crediting National WASP WWII Museum.