Thunderstorm Weather Hazards

AVIATION WEATHER

CHAPTER FOUR

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.

Dissipating Stage

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.

Updrafts

Downdrafts

Hazards

√

Cumulus

√

Mature

√

Dissipating

Figure 4-1 Summary of Thunderstorm Stage Characteristics

406.

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.

Turbulence

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.

Thunderstorms

4-3