As a weather spotter, and the card to prove it, get your ass down!!! Usually the sirens won't sound unless a funnel is sighted on the ground by a storm spotter, or there is rotation in a cloud which is formed for a tornado. There is a town about 20 miles from here that was hit last year with no warning, only 2 people were killed. If the siren goes off, that is your warning. Heed it.