SIGMET

SIGMET, or Significant Meteorological Information, is a weather advisory that contains meteorological information concerning the safety of all aircraft. There are two types of SIGMETs, convective and non-convective. The criteria for a non-convective SIGMET to be issued are severe or greater turbulence over a 3,000-square-mile (7,800 km²) area, or severe or greater icing over a 3,000-square-mile (7,800 km²) area or IMC conditions over a 3,000-square-mile (7,800 km²) area due to dust, sand, or volcanic ash [1].

This information is usually broadcast on the ATIS at ATC facilities. A SIGMET is a forecast valid for up to four hours. They are assigned an alphabetic designator from N (November) through Y (Yankee), excluding S and T. [2]

A Convective SIGMET is issued for convection over the Continental U.S. Convective SIGMETs are issued for an area of thunderstorms affecting an area of 3,000 square miles (7,800 km²) or greater, a line of thunderstorms at least 60 nm long, and/or severe or embedded thunderstorms affecting any area that are expected to last 30 minutes or longer. A Convective SIGMET is valid for 2 hours and they are issued every hour + 55 min. [3]

See also

• AIRMET
• PIREP