Definition
A report of actual weather conditions encountered by a pilot in flight, transmitted by radio to a ground facility (typically Flight Service) and then disseminated to other pilots, controllers, and forecasters. A PIREP includes items such as location, time, altitude, sky cover, visibility, temperature, wind, turbulence, icing, and any other significant weather observed.
Plain English
A short weather report from a pilot describing what the weather is actually like up where they are flying, so other pilots and forecasters know what's really happening in the air.
Context Anchor
You may hear, give, or read pilot weather reports during weather briefings, radio calls, and flight planning.
Derivation
Short for 'pilot report.' The value comes from the source: forecasts and ground-based observations describe what should be happening, while a pilot report describes what is actually happening at flight altitude.
Why Pilots Care
Supplies real-time observations that forecasts often miss, allowing better decisions about route, altitude, and safety.
Intuition Check
Do not read this as any report written by a pilot. In weather use, it means an in-flight observation of actual weather conditions shared for aviation use.
Example Sentence 1
After breaking out on top at 8,000 feet, the pilot gave Flight Service a PIREP reporting cloud tops and smooth air above the layer.
Example Sentence 2
The briefer passed along recent pilot reports showing clear air and no icing over the destination.