Figure 5-1.-Location of electric charges inside a typical thunderstorm cell.
conditions listed below are generally representative of
many (but not necessarily all) thunderstorms.
. The chance of severe or extreme turbulence
within thunderstorms is greatest at higher altitudes, with
most cases of severe and extreme turbulence about
8,000 to 15,000 feet above ground level (AGL). The
least turbulence may be expected when flying at or just
below the base of the main thunderstorm cloud. (The
latter rule would not be true over rough terrain or in
mountainous areas where strong eddy currents
produced by strong surface winds would extend the
turbulence up to a higher level.)
l The heaviest turbulence is closely associated
with the areas of heaviest rain.
. The strongest updrafts are found at heights of
about 10,000 feet AGL or more; in extreme cases,
updrafts in excess of 65 feet per second occur.
5-3
Downdrafts are less severe, but downdrafts on the order
of 20 feet per second are quite common.
l The probability of lightning strikes occurring is
greatest near or slightly above the freezing level.
Because of the potential hazards of flying in a
thunderstorm, it is obviously nothing short of folly for
pilots to attempt to fly in thunderstorms, unless
operationally necessary.
THUNDERSTORM SURFACE
PHENOMENA
The rapid change in wind direction and speed
immediately before thunderstorm passage is a
significant surface hazard associated with thunderstorm
activity. The strong winds that accompany
thunderstorm passage are the result of horizontal
spreading of downdraft currents from within the storm
as it approaches the ground.
