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(3) Frequently hail is carried aloft by updrafts and thrown out of the top or sides of the
clouds; it may be encountered in clear air several miles from the thunderstorm. Most
thunderstorms have hail in the interior of the cumulonimbus cloud. In a large percentage of
the cases, the hail melts before reaching the ground, but this does not make it any less of a
danger to the pilot who may encounter it aloft.

c. Lightning. The electricity produced by a thunderstorm is rarely a great hazard to
the structure of an aircraft, but its general hazards include:

(1) Temporary loss of vision at night due to the sudden flash of light.

(2) Damage to the electronic equipment.
(3) Holes in the aircraft exterior covering due to actual hits by lightning.

d. Icing. Clear ice accumulation in thunderstorms above the freezing level can be so
rapid that an aircraft may become incapable of keeping its altitude and/or attitude.

e. Precipitation/Low Ceiling and Visibility. A thunderstorm contains considerable
amounts of liquid water, but this moisture is not necessarily falling to the earth as rain. Water

drops are carried aloft by the updrafts or may be held in the updrafts so that visibility is

reduced to near zero in the thunderstorm.

When rain showers do fall to the earth, they are usually heavy enough to cause low

ceilings and poor visibility. Also, dust between the base of the cloud and the ground may

cause an additional decrease in visibility.

f. Effect on Altimeters. Pressure usually falls rapidly with the approach of a thunderstorm.

It then raises quickly with the arrival of the first gusts, the cold downdrafts, and the heavy

rain showers. The pressure then returns to the original pressure as the rain ends and the
storm moves on. This cycle of pressure change may occur over a period of 15 minutes.

Altitude indicated on the altimeter during the heavy rain may be wrong by over a hundred

feet a few minutes after the rain stops.

g. Surface Winds

(1) The horizontal outward movement of the downdrafts in the area unde a thunderstorm
causes a rapid change in wind direction and speed (low-level wind shear) in the area around
the thunderstorm. The gusty shifting winds are usually hazardous to landing aircraft.