Acronym for &Pilot Report&. Acts as a means for one pilot to pass on current, potentially useful information to other pilots such as turbulence. Pireps are essential to maintaining a real-time weather picture for both the pilot and the controller. The importance of PIREP's is to provide inflight advisories, and weather avoidance information to en route aircraft. The Air Traffic Control Tower uses the reports to expedite the flow of air traffic in the vicinity of the field and for hazardous weather avoidance procedures. The Air Route Traffic Control Center uses the reports to expedite the flow of en route traffic, to determine most favorable altitudes, and to issue hazardous weather information within the center's area. The National Weather Service uses the reports to verify or amend conditions contained in aviation forecast and advisories. The National Weather Service, other government organizations, the military, and private industry groups also use Pireps for research activities in the study of meteorological phenomena. FAA facilities are required to solicit Pireps when the following weather conditions exist, are reported, or forecast to occur: Ceilings at or below 5000 feet, visibility on surface or aloft is reported at less than 5 miles, turbulence of moderate degree or greater, icing of light degree or greater, windshear, volcanic ash clouds.