Reported May 2006

BACKGROUND: The National Oceanic and Atmospheric Administration, or NOAA, will implement an Enhanced Fujita Scale (EF) to rate the severity of tornadoes. The new scale will replace the original Fujita scale, which was originally developed for wooden structures. The enhanced scale will still run from zero to five, however, ranges in wind speed will be more accurate with the improved rating scale and will also take into account the type of structure. For instance, winds moving at 100 MPH would do different damage to a house than it would to a concrete building or a strip mall.

THE FUJITA SCALE: The F Scale was developed in 1971 by Theodore Fujita to rate tornadoes and estimate their wind speed based on the damage they cause. The original scale's limitations, however, may have led to inconsistent ratings, including possible over-estimates of wind speeds. The new EF scale incorporates more damage indicators and degrees of damage to provide a more detailed analysis and better correlation between damage and wind speed.

ABOUT TORNADOES: A tornado begins with a thunderstorm cloud that can build up a lot of energy. If this energy creates a particularly strong updraft of air it will form a vortex, much like how a whirlpool forms in a bathtub that is draining. The air is pulled toward the center in a spiral, forming a tornado under the thundercloud. Wind speeds can reach 200 MPH to 300 MPH, and if the dangling vortex touches ground, the combination of the whirling wind's speed, the updraft and pressure differences can cause severe damage. The path of the parent thundercloud determines the path of a tornado, but it will often appear to hop (called a "jumper"). This occurs when the vortex is disturbed, causing it to collapse momentarily and reform.

The American Meteorological Society contributed to the information contained in the TV portion of this report.

If you would like more information, please contact:

Dr. Joe Schaffer NOAA / National Weather Service
National Centers for Environmental Prediction
Storm Prediction Center
1313 Halley Circle
Norman, OK 73069 U.S.A.
spc.feedback@noaa.gov

For more information on weather phenomena and meteorology:

The American Meteorological Society
45 Beacon Street
Boston, MA 02108-3693
617-227-2425
http://www.ametsoc.org

FACTOID...

On May 27, 1896, the Great Cyclone of St. Louis killed at least 300 people and injured more than 1,000. The storm also razed large chunks of the city.

ON THE WEB...

www.spc.noaa.gov/efscale