BIRMINGHAM, Ala. — Severe thunderstorms dumped heavy rains across the Southeast on Monday and caused flash flooding in central Alabama, where crews in small boats and military trucks had to rescue dozens of people from their homes and cars. In Mississippi, police and volunteers searched for a 9-year-old girl who was swept away after the storms dropped nearly 7 inches of rain there over the last two days. A possible tornado in another part of the state damaged homes and hurt seven people, and a motorist in metro Atlanta was found dead after driving into a creek swollen with rainwater.