How long is one valid
4 hours
Types of Sigmets
Severe Icing not associated with thunderstorms
Severe or Clear air turbulence
Dust Storms lowering vis below 3 miles
Convective Sigmet Types and validity
Valid for 2 hours
Severe thunderstorms
Hail greater than 3/4 inch
Tornadoes
Embedded thunderstorms
Squall line