
The unusual outbreak of night tornadoes in the U.S. Midwest Wednesday morning may have been triggered by a warm winter, an expert says.
The twister outbreak, which started soon after midnight in Kansas, killed at least 13 people in southern Illinois, northern Missouri, and western Tennessee.
The most powerful tornado touched down in Harrisburg, Illinois, with winds of about 180 miles (289 kilometers) an hour. (Learn what happens inside a twister.)
"It'd be fair to say an unusually warm winter was probably a major factor [in causing the tornadoes]," said Jeff Masters, director of the meteorological website Weather Underground.
"You get far fewer tornadoes in February during cold winters."










