Definition
A PIREP is a report of actual weather conditions encountered in flight, made by a pilot and passed to a ground facility (such as Flight Service or ATC) for distribution to other pilots and forecasters. It typically includes location, time, altitude, aircraft type, and observed conditions such as cloud bases and tops, in-flight visibility, turbulence, icing, wind, and temperature.
Plain English
A short weather report from a pilot in the air, telling people on the ground what the weather is actually like up there right now.
Context Anchor
You will see PIREPs in preflight weather briefings, aviation weather displays, and in-flight weather updates when pilots report actual conditions along a route.
Derivation
PIREP is a contraction of 'pilot report.' The 'PI' is from pilot and 'REP' from report — the same shorthand pattern used in METAR (meteorological aerodrome report) and SIGMET. Knowing it simply means 'pilot report' makes the term self-explanatory in conversation and on charts.
Why Pilots Care
Gives pilots real-time weather details from aircraft already in the air that may not yet appear in forecasts.
Intuition Check
A PIREP is not a forecast. It is an actual observation from a pilot in flight.
Example Sentence 1
After breaking out on top at 9,000 feet, the pilot called Flight Service and filed a PIREP reporting cloud tops at 8,500 and smooth air above.
Example Sentence 2
Controllers relayed the latest PIREP to warn following aircraft about possible turbulence.