The Deadliest Of Twisters

People in "Tornado Alley" say Tuesday's twister was the worst they've ever seen, and scientists fear it may be an F-5 category tornado on the Fujita Scale, the most powerful of all tornadoes.

F-5 tornadoes are rare, but when they hit, they bring 300 mph winds and unparalleled destruction, disintegrating buildings, and sending cars and truck through the air like missiles, CBS News Meteorologist Craig Allen reports.

They can occur in a variety of situations but are generated most often in severe thunderstorms that occur when warm air and cold air collide.

The collision forces warm air upward, and that creates a low pressure area at the ground. Surrounding air moves in to fill the vacuum.

In severe storms, cloud tops can rise high into the air, reaching the level of strong horizontal winds that blow the tops into the classic anvil shape often reported around tornadoes. When this happens, more air is pulled upward in something like a chimney effect.

The air moving in toward the "chimney" begins to turn counterclockwise and then rises in a twisting column of extreme violence.

Winds in a tornado are believed to reach more than 200 to 300 mph.

Normally tornadoes form in the rear portion of severe storms which move toward the east or northeast and are separate from the heavy rains that occur in these storms.

Tuesday's tornado in Oklahoma was at least a half-mile to one-mile wide, Allen says. The tornado was definitely an F-4, leaving a wide swath of destruction in its wake, but it may even be an F-5.

Of all the tornadoes that occur across the United States in a year (usually more than 1,000), fewer than 1 percent of them end up being F-4s or F-5s.