Honeywell Primus 880 Pilot's Manual page 141

PRIMUSr 880 Digital Weather Radar System
ICING
Updrafts in a thunderstorm support abundant liquid water with
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relatively large droplet sizes; and when carried above the freezing
level, the water becomes supercooled. When temperature in the
upward current cools to about - 15 _C, much of the remaining water
vapor sublimates as ice crystals; and above this level, at lower
temperatures, the amount of supercooled water decreases.
Supercooled water freezes on impact with an aircraft. Clear icing
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can occur at any altitude above the freezing level; but at high levels,
icing from smaller droplets may be rime or mixed with rime and clear.
The abundance of large, supercooled droplets makes clear icing
very rapid between O _C and - 15 _C and encounters can be
frequent in a cluster of cells. Thunderstorm icing can be extremely
hazardous.
DRY AIR
INFLOW
Schematic Cross Section of a Thunderstorm
Federal Aviation Administration (FAA) Advisory Circulars
A- 6
COLD
NAUTICAL MILES
0
Figure A- 1
MOTION OF STORM
WARM AIR INFLOW
AIR
OUTFLOW
WARM AIR
WAKE
WAKE
COLD
AIR
OUTFLOW
5 10
INFLOW
GUST FRONT
15
AD- 37561@
A28- 1146- 102- 00