AIM
5/19/22
g.
Current weather radar systems are able to
objectively determine precipitation intensity. These
precipitation intensity areas are described as “light,”
“moderate,” “heavy,” and “extreme.”
REFERENCE
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Pilot/Controller Glossary
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Precipitation Radar Weather Descriptions
EXAMPLE
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1.
Alert provided by an ATC facility to an aircraft:
(aircraft identification) EXTREME precipitation between
ten o’clock and two o’clock, one five miles. Precipitation
area is two five miles in diameter.
2.
Alert provided by an FSS:
(aircraft identification) EXTREME precipitation two zero
miles west of Atlanta V
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O
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R, two five miles wide, moving
east at two zero knots, tops flight level three niner zero.
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1
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27. Thunderstorm Flying
a.
Thunderstorm Avoidance. Never regard any
thunderstorm lightly, even when radar echoes are of
light intensity. Avoiding thunderstorms is the best
policy. Following are some Do’s and Don’ts of
thunderstorm avoidance:
1.
Don’t land or takeoff in the face of an
approaching thunderstorm. A sudden gust front of
low level turbulence could cause loss of control.
2.
Don’t attempt to fly under a thunderstorm
even if you can see through to the other side.
Turbulence and wind shear under the storm could be
hazardous.
3.
Don’t attempt to fly under the anvil of a
thunderstorm. There is a potential for severe and
extreme clear air turbulence.
4.
Don’t fly without airborne radar into a cloud
mass containing scattered embedded thunderstorms.
Scattered thunderstorms not embedded usually can
be visually circumnavigated.
5.
Don’t trust the visual appearance to be a
reliable indicator of the turbulence inside a
thunderstorm.
6.
Don’t assume that ATC will offer radar
navigation guidance or deviations around thunder-
storms.
7.
Don’t use data-linked weather next genera-
tion weather radar (NEXRAD) mosaic imagery as the
sole means for negotiating a path through a
thunderstorm area (tactical maneuvering).
8.
Do remember that the data
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linked NEXRAD
mosaic imagery shows where the weather was, not
where the weather is. The weather conditions
depicted may be 15 to 20 minutes older than indicated
on the display.
9.
Do listen to chatter on the ATC frequency for
Pilot Weather Reports (PIREP) and other aircraft
requesting to deviate or divert.
10.
Do ask ATC for radar navigation guidance
or to approve deviations around thunderstorms, if
needed.
11.
Do use data-linked weather NEXRAD
mosaic imagery (for example, Flight Information
Service-Broadcast (FIS-B)) for route selection to
avoid thunderstorms entirely (strategic maneuver-
ing).
12.
Do advise ATC, when switched to another
controller, that you are deviating for thunderstorms
before accepting to rejoin the original route.
13.
Do ensure that after an authorized weather
deviation, before accepting to rejoin the original
route, that the route of flight is clear of thunderstorms.
14.
Do avoid by at least 20 miles any
thunderstorm identified as severe or giving an intense
radar echo. This is especially true under the anvil of
a large cumulonimbus.
15.
Do circumnavigate the entire area if the area
has 6/10 thunderstorm coverage.
16.
Do remember that vivid and frequent
lightning indicates the probability of a severe
thunderstorm.
17.
Do regard as extremely hazardous any
thunderstorm with tops 35,000 feet or higher whether
the top is visually sighted or determined by radar.
18.
Do give a PIREP for the flight conditions.
19.
Do divert and wait out the thunderstorms on
the ground if unable to navigate around an area of
thunderstorms.
20.
Do contact Flight Service for assistance in
avoiding thunderstorms. Flight Service specialists
have NEXRAD mosaic radar imagery and NEXRAD
single site radar with unique features such as base and
composite reflectivity, echo tops, and VAD wind
profiles.
b.
If you cannot avoid penetrating a thunderstorm,
following are some Do’s before entering the storm:
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Meteorology