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Wintry Mix in the Great Lakes Region; Mountain Snow in the West

Heavy snow, a wintry mix, and strong winds are likely in the Upper Midwest and Great Lakes into the Interior Northeast this weekend. Heavy mountain snow will continue across the Pacific Northwest and in parts of the Northern and Central Rockies. Read More >

Seattle, WA

Center Weather Service Unit

ZSE SIGMETs

Weather.gov > Seattle, WA > ZSE SIGMETs

 

 

 


Text of all SIGMETs Around Contiguous Western US
None Found
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


Map of SIGMETs (including International)

 

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