Pilot weather reports (PIREPS) are weather observations provided by pilots.
PIREPs provide valuable information regarding the conditions as they actually exist in the air, which cannot be gathered from any other source. Pilots can confirm the height of bases and tops of clouds, locations of wind shear and turbulence, and the location of inflight icing. PIREPs are filed in a stand format: station identifier, type of report (routine or urgent), time, altitude/flight level, aircraft type, sky cover/cloud layers, weather, air temperature, wind, turbulence, icing and remarks. Below is an example.
KCMH UA /OV APE 230010/TM 1516/FL085/TP BE20/SK BKN065/WX FV03SM HZ FU/TA 20/TB LGT
Explanation: This a routine PIREP. The pilot is reporting from one zero miles southwest of Appleton VOR; the time of the report is 1516 UTC; the altitude is eight thousand five hundred; the aircraft type is a King Aire 200; the bases of a broken cloud layer is at six thousand five hundred; flight visibility 3 miles with haze and smoke; the air temperature is 20 degrees Celsius and there is light turbulence.
AIM 2018 7−1−20. Pilot Weather Reports (PIREPs)
FAA AC 00-45H Aviation Weather Services pg. 3-6
FAA-H-8083-25B Pilot’s Handbook of Aeronautical Knowledge pg. 13-8