| MILWAUKEE, Wis
MILWAUKEE, Wis A powerful storm system that moved through the nation's midsection over the weekend caused what may be a record-breaking seven tornadoes in Wisconsin, officials said Monday.
"It's one of the most significant tornado outbreaks in April," said Rich Mamrosh, meteorologist for the National Weather Service. He said if confirmed, the number of Sunday night storms may have broken a record for a single day in April in the state -- the previous record was six.
Mamrosh said a strong low pressure system moved from South Dakota to northern Wisconsin Sunday, moving warm, moist air into the state, which was followed by a cold front, producing the storms.
A tornado in Merrill in the north-central portion of the state causing widespread damage to homes and businesses, said Captain Scott Krause of the Merrill Fire Department. Three people were taken to area hospitals.
Storms caused damage in other portions of the Midwest and south over the weekend. Iowa governor Terry Branstad declared a state of emergency after a storm Saturday that destroyed over half the town of Mapleton, but left no one seriously injured among its 1,200 residents, according to local law enforcement.
The peak U.S. tornado season lasts from March until early July, the period when warm, humid air often has to thrust upward against cool, dry air.
Further south in Texas, thunderstorms, high winds and hail on Sunday night blew down trees, tore off roofs and left some traffic lights not working in the Dallas area, said Michelle Schuldt, a meteorologist with the National Weather Service.
In Prosper, a town of 10,500 located north of Dallas, golf ball-sized hail damaged a "tremendous number" of cars, according to fire chief Ronnie Tucker. Many houses and businesses in the town are missing west-facing windows, and a number of fences are down, Tucker said.
"It was a heck of a hail storm," he said.
Some Dallas-area schools canceled classes Monday because of a loss of electricity, including the Alvarado Independent School district.
Much of Tennessee faces rough weather Monday when a cold-front moves in after a weekend of record-breaking high temperatures.
High winds are expected to push into Memphis and West Tennessee by late morning, with the front moving across the state all day long.
Brittney Whitehead, meteorologist with the National Weather Service in Nashville, said the area faces a slight risk of severe thunderstorms and a 10 percent chance for tornadoes.
The storm front follows a weekend of unseasonably high temperatures, include a new record of 91 Saturday in Nashville. It was 86 Sunday.
(Reporting by John Rondy, Tim Ghianni and Corrie MacLaggan; Writing by Mary Wisniewski; Editing by Greg McCune)