Atmospheric Stability

CHAPTER TWO

AVIATION WEATHER

Towering cumulus are clouds nearing the thunderstorm stage. They can produce heavy rain

showers and moderate turbulence in and near the cloud. Icing is common above the freezing

level.

Cumulonimbus clouds are thunderstorm clouds. A cumulonimbus cloud is sometimes referred to

as a "CB." Cumulonimbus is an exceedingly dangerous cloud, with numerous hazards to flight

such as severe to extreme turbulence, hail, icing, lightning, and other hazards discussed in

Chapter Four. Figure 2-18 summarizes the weather conditions found in the various types of

clouds.

Cloud Groups

High Clouds

Middle Clouds

Low Clouds

Clouds with Extensive

Vertical Development

Visibility

Good to Fair

1/2 mile to a few feet

A few feet

Icing

None to Light

None to Moderate

None to

Severe

Moderate

Turbulence

None to Light

None to Moderate

None to

Severe

Moderate

Figure 2-18 Cloud Families

209.

ATMOSPHERIC STABILITY

One of the most important meteorological considerations to a pilot is stability. Atmospheric

stability is one of the primary determinants of weather encountered in flight. In some cases, a

pilot may be able to determine if stable or unstable conditions exist along the route of flight.

There are three conditions of stability: stable, neutral stable, and unstable. We will consider each

of these individually by observing a ball inside a bowl. If the ball is displaced, and tends to

return to its original position, the ball is said to be stable (Figure 2-19).

TENDENCY TO RETURN

Figure 2-19 Stable

2-20 Atmospheric Mechanics of Winds, Clouds and Moisture, and Atmospheric Stability