The Atmosphere
Movement in the Atmosphere
Atmospheric Stability
Localised Winds
Clouds
Fronts
Visibility and Fog
Aircraft Icing
Thunderstorms
Altimetry
Weather Reports and Forecasts
Practice Exam

Thunderstorm Formation

Conditions for Thunderstorm Formation

Three things are needed for a thunderstorm to form:

A Deeply Unstable Atmosphere
High Humidity
Without sufficient water vapour in the atmosphere, large & well developed cumuliform clouds will not exist
A Trigger
Some action must occur that causes the initial lifting of the surface air. Once it has been lifted, the stability of the atmosphere determines if it will continue rising.

Thunderstorm Triggers

Cumulonimbus clouds are often referred to by the trigger they as associated with. These cumulonimbus types include:

Convective Thunderstorms

Thunderstorms that are a result of convection. The sun heats the surface (solar radiation) and the warm, humid air rises in an unstable atmosphere.

Frontal Thunderstorms

Thunderstorms that form along a front after cold air forces a warmer airmass to rise rapidly.

Orographic Thunderstorms

Thunderstorms that develop after air is forced up a mountainside. These cumulonimbus usually have the help of convection as well.

Convergence Thunderstorms

Thunderstorms that develop in a convergence, where two airmasses are colliding head-on and the air is forced to rise.