AIRMETs, or "Airman's Meteorological Information" (WA), report weather events that are considered of operational interest to all types of aircraft. An AIRMET can be issued for such phenomena as moderate icing, moderate turbulence, high surface winds (more than 30 mph), IFR conditions affecting a geographic area, and mountain obscurement. As such, AIRMETs are of particular interest to General Aviation aircraft, many of which are not equipped to fly in Instrument Meteorological Conditions (IMC) or sustain adverse conditions.
SIGMETs, or "Significant Meteorological Information" (WS), concern weather events other than convective activity that are considered hazardous to all types of aircraft. This can include severe icing, severe/extreme turbulence, atmospheric storms (dust, sand, ash), and volcanic events. Convective SIGMETs (WST) report convective activity considered hazardous to all aircraft, including thunderstorms, tornadoes, hail, and severe wind gusts.
To visit the Aviation Weather Center's online graphical AIRMET page, click here. The current national AIRMET image is below.