Definition

a local storm, always produced by a cumulonimbus cloud, and always accompanied by lightning and thunder, usually with strong gusts of wind, heavy rain, and sometimes with hail. 

How to develop 

Unstable air, high moisture, and uplifting force are all required for thunderstorm to form  

3 stages of thunderstorm

• Cumulus is marked by a large billowing clouds with extensive vertical development, which is caused by updrafts from surface heating, terrain, pressure system or fronts 
• Mature is marked by the beginning of rain at the surface. During this stage, updrafts are at their maximum and extreme vertical shearing occurs between the updrafts and the cooler downdrafts following the precipitation 
• Dissipating is marked by downdrafts. The cool downdrafts eventually terminate the uplifting forces. When the downdrafts end and the rain has stopped, this signifies the end of the dissipating stage

If a radar indicates thunderstorm activity, pilots should avoid the cells by at least 20 miles. 

Two different categories

• Airmass TS is generally caused by surface heating (at desert or sea) 
• Steady state TS is associated with weather systems and frontal movement 

Three principal types

• Single cell (=ordinary cell thunderstorms) consists of only one cell. It easily circumnavigated by pilots except at night or when embedded in other clouds. Single cell thunderstorms are rare. Almost all thunderstorms are multi-celled.  
• Multicell cluster and line consists of a cluster of cells at different stages of their life cycles. As the first cell matures, it is carried downwind, and a new cell forms upwind to take its place. A multicell may have a lifetime of several hours (or more), which makes it tougher to circumnavigate than a single-cell thunderstorm. May have supercells embedded within them.  
• Supercell consists primarily of a single, quasi-steady rotating updraft that persists for an extended period of time. Updraft speeds may reach 9,000 fpm (100 knots). They may persist for many hours (or longer) and their size and persistence make them tough to circumnavigate.