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Severe US Weather: Why this warning is different

Long before powerful storms began to roll through the Midwest Saturday afternoon, forecasters had warned of "life-threatening" tornadoes, thunderstorms and hail.

Here are some details on why these warnings — which came on Friday — were so unusual.

JUST HOW RARE? This marks the second time in U.S. history that the Storm Prediction Center has issued a high-risk warning more than 24 hours in advance.

WHAT HAPPENED LAST TIME: The first high-risk warning more than a day early came in April 2006, when nearly 100 tornadoes tore across the southeastern U.S. In all, a dozen people died and more than 1,000 homes were damaged in Tennessee.

WHY EARLIER WARNINGS: In the past, people often have had only minutes of warning when a siren went off. But improvements in storm modeling and technology let forecasters predict storms earlier and with greater confidence, the National Weather Service says. The Storm Prediction Center is part of the service.

NEW WARNING LANGUAGE: The weather service is now testing words such as "mass devastation," ''unsurvivable" and "catastrophic" aimed at getting more people to take heed. The warnings are being experimented with in Kansas and Missouri. The "life-threatening" warning for this round of storms, despite the dire language, was not part of that effort but just the most accurate way to describe what was expected, a weather service spokeswoman said.

ON THE GROUND: Tornadoes were spotted across the Midwest and Plains. Storms were reported in Kansas, Iowa, Nebraska and Oklahoma. Emergency officials in Iowa said a large part of the town of Thurman in the western part of the state was destroyed but no one was injured. A hospital in Creston, southwest of Des Moines, was damaged but patients and staff were not hurt. And a reported tornado in Wichita, Kan., caused widespread power outages and other damage, including to housing and at an Air Force base.

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Storm Prediction Center: http://www.spc.noaa.gov/