When are Convective SIGMETs (WSTs) issued?

Severe thunderstorms with 1.) winds greater than 50 knots 2.) hail at the surface greater than or equal to 3/4 inch in diameter 3.) tornadoes Embedded thunderstorms Lines of thunderstorms Thunderstorms with heavy or greater precipitation that affect 40% or more of a 3,00 sq mi or greater region