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A28-1146-102-00 FederalAviation Administration (FAA) Advisory Circulars
A-13
MAXIMUM STORM TOPS
Photographic data indicates that the maximum height attained by
thunderstormclouds is approximately 63,000 feet. Such very tall storm
tops have not been explored by direct means, but meteorological
judgments indicate the probable existence of large hail and strong
vertical drafts towithin afew thousand feet of the top of these isolated
stratosphere-penetrating storms. THEREFORE, IT APPEARS
IMPORTANT TOAVOID SUCH VERYTALL STORMS ATALL
ALTITUDES.
HAIL IN THUNDERSTORMS
TheoccurrenceofHAILISMUCH MORECLEARLYIDENTIFIEDWITH
THEINTENSITYOFECHOESTHANISTURBULENCE.AVOIDANCE
OFMODERATE AND SEVERE STORMS SHOULDALWAYS BE
ASSOCIATEDWITHTHEAVOIDANCEOFDAMAGINGHAIL.
VISUAL APPEARANCE OF STORM AND ASSOCIATED
TURBULENCE WITH THEM
On numerous occasions, flight at NSSL have indicated that NO
USEFUL CORRELATION EXISTS BETWEEN THE EXTERNAL
VISUAL APPEARANCE OF THUNDERSTORMS AND THE
TURBULENCE AND HAIL WITHIN THEM.
MODIFICATIONOF CRITERIA WHEN SEVERE STORMS AND
RAPID DEVELOPMENT ARE EVIDENT
During severe storm situations, radar echo intensities may grow by a
factor of ten each minute, and cloud tops by 7,000 feet per minute.
THEREFORE, NO FLIGHT PATHTHROUGH AFIELD OF STRONG
OR VERYSTRONG STORMS SEPARATEDBY 20-30 MILES OR
LESS MAYBECONSIDEREDTOREMAIN FREE FROM SEVERE
TURBULENCE.