PIREPs, AIRMETs, SIGMETs and Winds Aloft

A pilot report, or PIREP, is the only direct observation of conditions aloft — tops, in-flight visibility, turbulence, and icing — and is coded UA for routine or UUA for urgent. Because it comes from a real airplane, it confirms or corrects the forecast, so pilots are urged to file them. AIRMETs and SIGMETs warn of en route hazards at different severities: an AIRMET covers hazards significant to light aircraft such as moderate turbulence, moderate icing, or widespread low visibility, while a SIGMET covers more severe hazards affecting all aircraft such as severe turbulence or severe icing. A convective SIGMET specifically covers thunderstorm hazards like embedded storms, lines of storms, and severe-or-greater turbulence. Winds and temperatures aloft forecasts use direction (true), speed in knots, and Celsius temperature; a group like 2416 means wind from 240 true at 16 knots, and speeds over 100 knots are coded by adding 50 to the direction.