National Weather Service United States Department of Commerce

Nestor Bringing Impacts to the Southeast; Strong Cold Front in the West

Post-tropical Storm Nestor will produce heavy rain with the potential for flash flooding, storm surge up to 4 feet, strong winds, and severe thunderstorms over Florida and parts of the Southeast. In the West, a cold front will produce mountain snow and strong winds. Fire weather threats remain critical in portions of southern California, the Great Basin, and High Plains. Read More >

 

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

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