Purdue Scientists Unravel Midwest Tornado Formation.

(From AScribe)

WEST LAFAYETTE, Ind. -- A Purdue University study of tornado formation indicates that twisters can develop in unexpected ways and at unexpected times and places, a discovery that presents a new twist to weather watchers across the country.

Although tornadoes are often conceived of as arising from springtime storms that develop in early evenings out of isolated weather cells, a new study spearheaded by Purdue's Robert "Jeff" Trapp indicates those conceptions often fail to hold, especially in the Midwest. Although far from the so-called "Tornado Alley," a region that falls generally in the plains of Texas, Oklahoma and Kansas, the Midwest still experiences a high number of the storms every year.

After examining data on more than 3,800 U.S. tornadoes, Trapp's team has found that many twisters develop within the line-shaped storm fronts that often sweep across the country. The twist is that these are tornadoes that are more likely to form late at night and in colder months.

"The upshot of our analysis is that tornadoes form under a broader set of circumstances than meteorologists once thought, and this is especially true if you live far from Tornado Alley," said Trapp, an associate professor of earth and atmospheric sciences in Purdue's College of Science. "If you're driving in the rain on an October midnight near Lake Michigan, remember that a tornado is not outside the realm of possibility."

Trapp's study, which he performed with colleagues at the University of Oklahoma, Colorado State University and the National Severe Storms Laboratory, appears in the February issue of the journal Weather and Forecasting. As a first step toward improving our ability to predict tornado strikes, which often come with only a few minutes' warning, the group initially set out to find what types of storms generally produce the destructive funnels.

"In the heart of Tornado Alley, tornadoes most often develop from relatively small 'cell' storms that look like blotches on a Doppler radar weather map," Trapp said. "Over time, these cells frequently merge into line-shaped storms that can stretch hundreds of miles. The conventional wisdom has been that line storms don't often spawn tornadoes, but we found that a significant number did."