(April 25, 2007) - After the tornadoes touchdown, the debris fields settle and the blare of outdoor warning sirens are replaced by the sounds of chain saws and wood chippers - you'll find National Weather Service meteorologists out walking the tracks and assessing the damage. With more than 500 tornadoes reported so far this year, they have been quite busy, especially in the southern plains and southeastern states.

At this time of year, it is certainly not unusual to see a series of upper level storm systems pushing through the southern Rockies and triggering powerful tornadic supercells over eastern New Mexico, western Texas and Oklahoma. These powerful storms frequently leave death and destruction in their wake as they move eastward. Preliminary reports show at least 60 people have been killed by tornadoes so far this year. To date, most of those deaths have occurred in Florida (21), Alabama (10), Georgia (9) and Texas (8).

Since February 1, National Weather Service tornado assessment teams have been using a new, Enhanced Fujita (EF) scale to rate tornadoes and estimate wind speed based on damage. The EF scale refines and improves the original Fujita scale which was developed in 1971 by T. Theodore Fujita, Ph.D. Limitations of the original Fujita scale may have led to inconsistent ratings, including possible overestimates of associated wind speeds. The EF scale incorporates more damage indicators and degrees of damage than the original Fujita scale, allowing more detailed analysis and better correlation between damage and wind speed.

The original Fujita scale historical data base will not change. An F5 tornado rated years ago is still an F5, but the wind speed associated with the tornado may have been somewhat less than previously estimated. A correlation between the original Fujita scale and the EF scale has been developed. This makes it possible to express ratings in terms of one scale to the other - thereby preserving the historical database.