Definition
A report of actual weather conditions encountered by a pilot in flight, transmitted to a ground facility (typically Flight Service or ATC) for distribution to other pilots, forecasters, and controllers. A PIREP includes items such as location, time, altitude, sky condition, visibility, temperature, wind, turbulence, icing, and any other significant weather observed.
Plain English
It's a short message a pilot sends from the air describing what the weather is actually doing where they are flying, so other pilots and forecasters know what to expect.
Context Anchor
You will see pilot reports in weather briefings, instrument flight planning, aviation weather products, and radio calls to air traffic control or Flight Service.
Derivation
PIREP is a shortened aviation form of pilot report: “PI” comes from pilot and “REP” comes from report. That helps because the term means exactly that in aviation: a report made by a pilot about real conditions observed in flight.
Why Pilots Care
Provides real-time weather observations that help other pilots avoid hazards such as turbulence or icing.
Intuition Check
A pilot report is not just any paperwork a pilot fills out. In this context, it means a shared report of actual in-flight conditions.
Example Sentence 1
After breaking out on top at 8,000 feet, she gave Flight Service a PIREP noting the cloud tops and smooth ride above the layer.
Example Sentence 2
ATC used the PIREP about cloud tops to advise the next aircraft on climbout.