Government revises tornado ratings scale


Thursday, February 2nd 2006, 11:51 am
By: News On 6


ATLANTA (AP) _ The government is adopting a new classification system to rate the power of tornadoes, one in which estimated wind speeds are more closely aligned with actual damage, the National Weather Service announced Thursday.

The new system will go into effect in early 2007, officials said. They announced the change during the American Meteorological Society meeting in Atlanta.

Under the current system, known as the Fujita scale, an F-5 tornado _ considered the most powerful _ was capable of destroying a typical frame house, with wind speeds estimated at 261 mph to 318 mph. In the years since that was created in 1971, engineering studies have shown that much lower-speed winds could cause the same damage.

Under the new system, for a tornado to be classified as an F-5, the wind speeds would have to be at least 200 mph.

The old system rated tornadoes only based on damage to homes. The new system classifies tornadoes based on damage to 18 other types of structures, including trees, mobile homes and other types of buildings.