Definition
A PIREP is a report of actual weather conditions encountered by a pilot in flight, transmitted to a ground facility (typically Flight Service) and disseminated to other pilots, controllers, and forecasters. PIREPs include items such as location, time, altitude, sky condition, visibility, temperature, wind, turbulence, icing, and any other significant weather observed. They supplement official forecasts and surface observations by providing real-time, in-flight weather data from the only source that can directly observe conditions aloft.
Plain English
A short weather report made by a pilot describing what the air and sky are actually like at their altitude right now, then shared so other pilots and forecasters know what to expect.
Context Anchor
Seen in aviation weather briefings, weather products, and radio calls when pilots report or review real conditions along a route.
Derivation
PIREP is a contraction of 'pilot report.' The 'pilot' part identifies who is reporting; the 'rep' part is short for 'report.' The name reflects the core idea: the data comes directly from a pilot, not from a ground sensor or forecast model.
Why Pilots Care
Provide real-time, in-flight weather data that official forecasts may not capture, helping pilots avoid hazards like icing or severe turbulence.
Analogy
A PIREP is like a road-condition report from a driver ahead of you. The forecast may say what should be happening, but the person already there can tell you what is actually happening.
Intuition Check
Do not treat a PIREP as a forecast. A PIREP is an actual report from a pilot who observed the conditions in or near flight.
Example Sentence 1
After encountering moderate turbulence at 8,000 feet, the pilot called Flight Service and filed a PIREP so other aircraft in the area would be aware.
Example Sentence 2
Checking PIREPs before departure revealed icing conditions along the route.