Fly under the storm.
If it is not possible to avoid the storm(s), fly through the lower 1/3 of the storm.
When thunderstorms are isolated, they are easily circumnavigated provided the surrounding area
is clear of masking clouds. If lines of thunderstorms are present or if masking clouds obscure the
area around the storm, other techniques must be employed.
Circumnavigation presents no special flight problems. When the aircrew determines
circumnavigation is possible, they merely alter course to take them around the storm
(Figure 4-10). Since most individual thunderstorm cells are about five to ten miles in diameter,
detouring to one side or another would not appreciably add to either the time or distance of the
flight. In case of a line of thunderstorms, it is sometimes possible to circumnavigate them by
flying through thin spots of precipitation between the storms. Exercise care in this procedure
because another thunderstorm may lie on the other side of a thin spot.
Figure 4-10 Around a Thunderstorm
Over the Top
When circumnavigation of thunderstorms is not possible, the next best course of action is to go
over the top (Figure 4-11). Realize, thunderstorms build to great heights and this procedure is
restricted to aircraft with the capability and fuel to climb to these altitudes. Some turbulence
may be encountered in the clear air above the cloud. Additionally, hail can be thrown out the top
of the cumulonimbus cloud. Thus, allow a margin of safety by choosing an altitude separation
from the top of the thunderstorm of 1000 feet for every ten knots of wind speed at the altitude of
the tops. Oftentimes, aircraft cannot climb over the top of the cloud, but it will still be possible
to fly over the saddlebacks between the build-ups.