"As you get into the nighttime hours and you don't have that lift to maintain all that air at the top of the thunderstorm, then the primary force is gravity," Null says. "This heavy air is going to be coming down to the earth and it spreads out like an upside down mushroom."
Meteorologists are baffled by wind gusts that ripped through concentrated parts of the Bay Area early Monday morning while other areas remained completely still.