Tornado warnings were issued in Tennesee and Kentucky this morning, and three tornadoes had been reported by 4:35 a.m. Severe-weather warnings are in effect for the areas between New Orleans and Jacksonville, Fla., in the south and between Baltimore and Pittsburgh in the north. More than 13,000 people lost power when the storms tore through Memphis and four inches of rain fell over three hours. Downed power lines caused a grass fire in Arlington, Tenn. The storms are part of an unusual weather pattern this year fueled by winds blowing unseasonably warm air from the Gulf of Mexico into cold air coming over the plains from Canada. “It's not a normal weather pattern for this time of year,” one expert said.