On Sunday, it was 63 degrees. Many were skeptical that accumulating snow would fall the next day. But by Monday afternoon, five to 10 inches or more of cement-like snow had plastered large parts of the region. More than a half-million customers in Virginia and Maryland lost power because the weight of the snow combined with strong winds brought down tree limbs and power lines, and traffic on Interstate 95 came to a standstill. More than 12 hours later, many motorists are still stranded there.