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Tornado Climatology of the Contiguous
United States
(NUREG/CR-4461, Rev. 2)
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Publication Information
Manuscript Completed: December 2006
Date Published: February 2007
Prepared by
J.V. Ramsdell, Jr.
J.P. Rishel
Pacific Northwest National Laboratory
P.O. Box 999
Richland, WA 99352
A.J. Buslik, NRC Project Manager
Prepared for
Division of Risk Assessment and Special Projects
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001
NRC Job Code N6337
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Abstract
Characteristics of tornadoes reported in the contiguous United States from January 1950 through
August 2003 have been used to determine tornado strike probabilities and maximum wind speeds for use
in nuclear power plant design. Maps have been prepared that show the distribution of tornado events and
design wind speeds. Appendices contain the number of tornadoes and estimates of strike probabilities
and maximum wind speeds by 1°, 2°, and 4° latitude and longitude boxes.
The methods used in this analysis are identical to those used in the analysis leading to publication of the
tornado climatology in NUREG/CR-4461, Rev. 1. The primary difference between the climatology
presented here and the climatology in Rev. 1 is that wind speed estimates in this climatology are based on
the Enhanced Fujita Scale that correlates wind speeds with damage caused by tornadoes. These wind
speeds are significantly lower than the wind speeds in the original Fujita Scale. A second difference is
that the wind speeds in the Enhanced Fujita Scale are nominally 3-second average wind speeds, whereas
the wind speeds in the original Fujita Scale were nominally the fastest quarter-mile wind speeds. The
National Weather Service intends to implement the Enhanced Fujita Scale by February 2007.
The results of this analysis indicate that a maximum wind speed of about 230 mph is appropriate for
tornadoes with a best estimate probability of 10-7 per year for the central portion of the United States; a
maximum wind speed of 200 mph is appropriate for a region of the United States along the east coast, and
the western great plains; and a maximum wind speed of 160 mph is appropriate for the western United
States. Corresponding wind speeds in NUREG/CR-4461, Rev. 1, were 300 mph, 260 mph, and 200 mph,
respectively.
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