CFI Brief: Thunderstorms

An important aspect of becoming a private pilot is having an understanding of weather. Even more important is having a thorough understanding of weather that could pose a potential risk to flight. The goal of this understanding is so you can identify and avoid these hazardous conditions as part of your preflight preparations and inflight decision-making.

Thunderstorms are one such risk you should know and understand. Monday’s post went over this weather hazard in depth. Today, I will recap some of the more important information that the FAA Private Pilot Knowledge Exam tests.

Thunderstorms present many hazards to flying. Three conditions are necessary to the formation of a thunderstorm:

  1. Sufficient water vapor;
  2. An unstable lapse rate; and
  3. An initial upward boost (lifting).

The initial upward boost can be caused by heating from below, frontal lifting, or by mechanical lifting (wind blowing air upslope on a mountain).

There are three stages of a thunderstorm: the cumulus, mature, and dissipating stages. See the figure below.


The cumulus stage is characterized by continuous updrafts, and these updrafts create low-pressure areas. Thunderstorms reach their greatest intensity during the mature stage which is characterized by updrafts and downdrafts inside the cloud. Precipitation inside the cloud aids in the development of these downdrafts, and the start of rain from the base of the cloud signals the beginning of the mature stage. The precipitation that evaporates before it reaches the ground is called virga. The dissipating stage of a thunderstorm is characterized predominantly by downdrafts.

Lightning is always associated with a thunderstorm.

Hail is formed inside thunderstorms by the constant freezing, melting, and refreezing of water as it is carried about by the up- and downdrafts.

A pilot should always expect the hazardous and invisible atmospheric phenomena called wind shear turbulence when operating anywhere near a thunderstorm (within 20 NM).

Thunderstorms that generally produce the most intense hazard to aircraft are called squall-line thunderstorms. These non-frontal, narrow bands of thunderstorms often develop ahead of a cold front. Embedded thunderstorms are those that are obscured by massive cloud layers and cannot be seen.

Using the knowledge learned in this week’s weather posts on Thunderstorms, see if you can accurately answer the four sample knowledge test questions below.

1. What conditions are necessary for the formation of thunderstorms?
A—High humidity, lifting force, and unstable conditions.
B—High humidity, high temperature, and cumulus clouds.
C—Lifting force, moist air, and extensive cloud cover.

2. Thunderstorms reach their greatest intensity during the
A—mature stage.
B—downdraft stage.
C—cumulus stage.

3. Thunderstorms which generally produce the most intense hazard to aircraft are
A—squall line thunderstorms.
B—steady-state thunderstorms.
C—warm front thunderstorms.

4. A nonfrontal, narrow band of active thunderstorms that often develop ahead of a cold front is known as a
A—prefrontal system.
B—squall line.
C—dry line.

Answers and Explanations. 

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