Thunderstorms—Don’t Flirt...Skirt ‘Em
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In the limited state thunderstorm, the mature stage is self-destructive until the updraft will no longer support
the raindrops and precipitation begins to fall through the updraft. The buoyancy of the air is decreased until the
updraft becomes a downdraft. The cool precipitation tends to cool the lower portion of the cloud and, with its
“fuel supply” thus cut, the cell loses its energy and the storm dissipates. When all water droplets have fallen from
the cloud, the dissipating stage is complete.
If, in the mature stage, the updraft and downdraft areas remain equally balanced, the mature stage may then
become a “steady state” thunderstorm cell in which extreme turbulence and large hail may predominate. The
limited state thunderstorm cell may last from 20 minutes to 1.5 hours, while the steady state thunderstorm may
last as long as 24 hours and travel for 1,000 miles.
Although pilots have flown through limited state thunderstorms with little or no damage to the aircraft or
passengers, these pilots should consider themselves extremely fortunate to be alive. Any thunderstorm is an
uncontrolled heat engine that may produce any or all of the most violent weather hazards (for example, hail, ice,
turbulence) that a pilot will ever encounter.
Thunderstorm Avoidance
General Rules
Pilots should observe the following rules for any flight routed even potentially near actual or possible thunder-
storm activity:
• Avoid all thunderstorms.
• Never go closer than 5 miles to any visible storm cloud with overhanging areas, and strongly consider increas-
ing that distance to 20 miles or more. You can encounter hail and violent turbulence anywhere within 20 miles
of very strong thunderstorms.
• Do not attempt flight beneath thunderstorms, even when visibility is good, because of the destructive potential
of shear turbulence in these areas.
• At the first sign of turbulence, reduce airspeed immediately to the manufacturer's recommended airspeed for
turbulent air penetration for a specific gross weight (that is, maneuvering speed, or Va).
• If the aircraft inadvertently penetrates the thunderstorm, maintain a straight and level altitude on a heading that
will take you through the storm area in the minimum time.
• Never let compulsion take the place of good judgment.