average cell grows to a height of 25,000 feet during this stage. At higher latitudes, tops may be
as low as 12,000 feet.
Downdrafts continue to develop while the updrafts continue to weaken during the mature stage.
As a result, the entire thunderstorm cell becomes an area of downdrafts with precipitation in the
dissipating stage (Figure 4-1). Thunderstorms begin to dissipate when the updrafts, which are
necessary to produce condensation and the resulting release of heat, are no longer present.
During this stage the strong winds aloft may carry the upper section of the cloud into the familiar
anvil form. However, the appearance of an anvil does not indicate the thunderstorm is free of
hazards. Severe weather is present in many storms with a well-developed anvil.
Figure 4-1 Summary of Thunderstorm Stage Characteristics
THUNDERSTORM WEATHER HAZARDS
Some or all of the following hazards accompany thunderstorms: extreme turbulence, hail,
microbursts, severe icing, lightning, and tornadoes. Turbulence is the worst hazard and hail is
the second worst.
Severe turbulence is present in all thunderstorms. One of the major characteristics of every
thunderstorm is updrafts and downdrafts that can occur near each other creating strong, vertical
shear and turbulence. This turbulence can extend over 5000 feet above the cloud tops and down
to the ground beneath the cloud base. It can damage an airframe and cause serious injury to
passengers and crew.
The first gust or gust front, a low level turbulent area between the cold downdrafts of a
thunderstorm and the surrounding air of an approaching thunderstorm, is another form of
turbulence that can cause a rapid and drastic change in the surface wind (Figure 4-2). An attempt
to takeoff or land with an approaching thunderstorm nearby could have disastrous results. Gust
fronts can travel 5 to 20 miles from the thunderstorm.