National Weather Service United States Department of Commerce

Snow Will Persist in the Northeast and Great Lake States

Heavy Lake Effect snow will continue to the lee of the Great Lakes for the next couple of days. Snow will also return to the Northeast by Tuesday as another front moves in. Bitter cold wind chills can be expected in the Upper Mississippi Valley. Freezing temperatures will even impact central Florida. Meanwhile, elevated fire weather conditions will persist in southern California. Read More >


Icing Convective Turbulence
Icing SIGMETs Convective SIGMETs Turbulence SIGMETs
IFR Volcanic Ash All

Text of all CONUS SIGMETs

Description of Convective and Non-Convective SIGMETs

SIGMETs are Inflight Weather Advisories for Significant Meteorological hazards. A SIGMET is "widespread" in that it covers an area of at least 3,000 square miles. Note that the particular hazard may be present in only a small portion of the area at any particular time. SIGMETS are issued for:
  • Severe Icing (not associated with thunderstorms -- otherwise, it is a Convective SIGMET)
  • Severe Turbulence (similarly, only if not associated with thunderstorms)
  • Duststorms and sandstorms lowering visibility to less than three miles
  • Volcanic Ash

Convective SIGMETs are issued for severe convective activity, which implies severe turbulence, severe icing, and low-level wind shear. Specifically:
  • Embedded thunderstorms
  • A line of thunderstorms
  • Thunderstorms with heavy precipitation affecting 40%+ of an area at least 3,000 square miles
  • Surface winds 50+ knots due to severe thunderstorm
  • Hail 3/4+ inches in diameter
  • Tornadoes