Government revises tornado ratings scale
Thursday, February 2nd 2006, 1:07 pm
By: News On 6
ATLANTA (AP) _ The government will use a new classification system to rate the power of tornadoes so the estimated wind speeds are more closely aligned with actual damage.
Under the old system created in 1971 an F5 tornado is the most powerful. The last F5 in the US was the May 3rd, 1999, tornado that hit central Oklahoma and killed 43 people.
Currently an F5 is capable of destroying a typical frame house with wind speeds estimated at 261 to 318 miles an hour. Under the new system an F5 has wind speeds of at least 200 miles an hour.
The change is being made because engineering studies now show much lower-speed winds can cause the same damage.
The National Weather Service announced the change Thursday at the American Meteorological Society meeting in Atlanta and the new system is to go into effect in February 2007.
The new system also classifies tornadoes based on damage to 19 types of structures, including trees, mobile homes and other buildings.