Honeywell Primus 880 Pilot's Manual page 148

PRIMUSr 880 Digital Weather Radar System
MAXIMUM STORM TOPS
Photographic data indicates that the maximum height attained by
thunderstorm clouds 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 to within a few thousand feet of the top of these isolated
stratosphere- penetrating storms. THEREFORE, IT APPEARS
IMPORTANT TO AVOID SUCH VERY TALL STORMS AT ALL
ALTITUDES.
HAIL IN THUNDERSTORMS
The occurrence of HAIL IS MUCH MORE CLEARLY IDENTIFIED WITH
THE INTENSITY OF ECHOES THAN IS TURBULENCE. AVOIDANCE
OF MODERATE AND SEVERE STORMS SHOULD ALWAYS BE
ASSOCIATED WITH THE AVOIDANCE OF DAMAGING HAIL.
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.
MODIFICATION OF 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 PATH THROUGH A FIELD OF STRONG
OR VERY STRONG STORMS SEPARATED BY 20- 30 MILES OR
LESS MAY BE CONSIDERED TO REMAIN FREE FROM SEVERE
TURBULENCE.
A28- 1146- 102- 00
Federal Aviation Administration (FAA) Advisory Circulars
A- 13