Definition
Localized storms produced by strong, rising columns of moist, unstable air that build into towering cumulonimbus clouds, typically accompanied by lightning, thunder, heavy rain or hail, severe turbulence, strong gusty surface winds, and rapid pressure changes.
Plain English
Powerful weather cells where warm, moist air rises hard and fast, creating tall storm clouds that bring lightning, heavy rain, violent winds, and dangerous turbulence.
Context Anchor
Pilots encounter thunderstorms in weather briefings, forecasts, radar displays, and in flight when deciding whether to delay, divert, or fly around weather.
Derivation
From 'thunder' (Old English 'þunor', the loud sound following lightning) and 'storm' (Old English 'storm', a violent disturbance of the atmosphere). The name describes only the audible feature, but in aviation the real concerns are the violent updrafts, downdrafts, and hail produced inside the cloud.
Why Pilots Care
These storms can cause loss of aircraft control, structural damage, and loss of situational awareness, making avoidance a primary safety decision.
Grounding Statement
Picture a tall, dark, anvil-topped cloud towering tens of thousands of feet high, with rain shafts beneath it and lightning flickering inside -- that whole column is a thunderstorm.
Intuition Check
Do not assume a thunderstorm is safe if the airplane can stay out of the rain. The dangerous air around a thunderstorm can extend outside the visible rain and cloud.
Example Sentence 1
The pilot diverted twenty miles off course to stay clear of a line of thunderstorms building along the route.
Example Sentence 2
During the approach briefing the crew noted building thunderstorms west of the airport and elected to hold until the cells passed.