Rare Night Tornadoes This Week Fueled By Warm Winter? Rare twister outbreak killed 13 people in U.S. Midwest. Figure 1 Rubble left by a night tornado surrounds a home in Harveyville, Kansas, on February 29. Willie Drye for Published March 1, 2012 The unusual outbreak of night 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 , killed at least 13 people in southern , northern , and western . The most powerful tornado touched down in Harrisburg, Illinois, with winds of about 180 miles (289 kilometers) an hour. () "It'd be fair to say an unusually warm winter was probably a factor [in causing the tornadoes]," said , director of the meteorological website Weather Underground. "You get far fewer tornadoes in February during cold winters." (See ) Warm Winter Fueled Night Tornadoes Tornadoes are formed from rotating thunderstorms that are set in motion by upper-level winds known as the jet stream. Only 12 percent of tornadoes form between midnight and 6 a.m., according to the . That's because temperatures start falling after sunset—depriving potential tornadoes of their primary ingredient: warm, moist air, which rises and creates atmospheric instability that spawns tornadoes.
Rare Night Tornadoes This Week Fueled By Warm Winter? Rare twister outbreak killed 13 people in U.S. Midwest. Figure 1 Rubble left by a night tornado surrounds a home in Harveyville, Kansas, on February 29. Willie Drye for Published March 1, 2012 The unusual outbreak of night 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 , killed at least 13 people in southern , northern , and western . The most powerful tornado touched down in Harrisburg, Illinois, with winds of about 180 miles (289 kilometers) an hour. () "It'd be fair to say an unusually warm winter was probably a factor [in causing the tornadoes]," said , director of the meteorological website Weather Underground. "You get far fewer tornadoes in February during cold winters." (See ) Warm Winter Fueled Night Tornadoes Tornadoes are formed from rotating thunderstorms that are set in motion by upper-level winds known as the jet stream. Only 12 percent of tornadoes form between midnight and 6 a.m., according to the . That's because temperatures start falling after sunset—depriving potential tornadoes of their primary ingredient: warm, moist air, which rises and creates atmospheric instability that spawns tornadoes.
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