Circumnavigation

AVIATION WEATHER

CHAPTER FOUR

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

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.

Thunderstorms

4-13