900 Tornadoes Since April the 1st: U.S. may see Record number of Tornadoes this Year - 29th Apr 2011

A rare and potent combination of cool air clashing with warm, humid weather and extreme winds at varying altitudes ignited the deadly tornadoes that ravaged the U.S. South this week, meteorologists said on Thursday.

"Everything you need for a tornado outbreak was in place," said David Imy, a meteorologist from the Oklahoma-based U.S. government Storm Prediction Center.

April is normally an active month for tornadoes across the region as spring sets in. But weather watchers said this month was on track to be record-setting.

AccuWeather.com said more than 900 tornadoes had been reported since April 1 in an onslaught of severe thunderstorms that has spawned flooding and deadly twisters in parts of the Midwest and Southeast.

On Wednesday, at least 164 tornadoes tore across a region that stretched from Mississippi to Virginia, flattening homes, flipping over cars and leaving a trail of destruction. The tornadoes and storms killed at least 284 people.

"This could turn out to be one of the worst years for severe weather and tornadoes in history," said Dan Kottlowski, expert senior meteorologist for AccuWeather.com. Read More