JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
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 to be discussed in
Chapter 4. Table 2-1 summarizes the weather conditions found in the various types of clouds.
Cloud Groups
High Clouds Middle Clouds Low Clouds
Visibility Good to Fair ½ mile to a few feet A few feet A few feet
Icing None to Light None to Moderate None to Moderate Severe
Turbulence None to Light None to Moderate None to Moderate Severe
Table 2-1 — Cloud Families
Clouds with Extensive
Vertical Development
ATMOSPHERIC STABILITY
One of the most important meteorological considerations to a pilot is that of stability or
instability. 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 2-17).
Figure 2-17 — Stable Equilibrium and Neutrally Stable Equilibrium
If a ball on a flat table is displaced, it will tend to remain in its new position and is said to be
neutrally stable (Figure 2-17). It will not have a tendency to return to its original position, or
move away from its final position.
Now, consider an inverted bowl with a ball balanced on top. Once the ball is displaced, it will
tend to move away from its original position, never to return, and the ball is said to be in an
unstable condition (Figure 2-18).
Version 3.2/Dec 08 2-17