State Ranking In Number of Events

August 21, 2008

F5 Tornado damage in Parkersburg, Iowa, May 25, 2008.

Tornado damage, Windsor, Colo.

Prior to 1990, the average number of tornadoes per year in the Continental US was 772. In the period from 1990 through 2007, the average was 1,215. The number of tornadoes reported is up over 50 percent.

TX 2,831

KS 1,616

FL 1,107

OK 1,098

NE 1,061

IL 1,001

IA 926

CO 809

MO 776

MS 762

AR 751

MN 730

AL 721

LA 661

ND 548

SD 534

NC 500

IN 479

GA 473

SC 423

TN 406

WI 382

Top Ten Cities by

Frequency of Tornadoes

The 10 cities or towns with the
highest TScales are as follows:

1. Denver, CO (100)*

2. Houston, TX (90)

3. Miami, FL (90)

4. Hollywood, FL (88)

5. Tampa, FL (79)

6. Lincoln, IL (75)

7. Lakeland, FL (75)

8. Little Rock, AR (75)

9. Cape Coral, FL (70)

10. Oklahoma City, OK (67)

*Not downtown, but a rural area
to the northeast.

Fujita Tornado Scale

FScale Windspeed(Mph)

F0 40-72

F1 73-112

F2 113-157

F3 158-206

F4 207-260

F5 261-318

Source: CDS Business Mapping LLC

Midwest States High on List for Numbers of Tornadoes

While a rural area to the northeast of Denver, Colo., tops the nation when it comes to metropolitan areas most prone to tornados, Texas leads the states in the average total number of tornadoes per year in the continental United States, according to Boston-based CDS Business Mapping LLC, an online hazard mapping firm (www. cdsys.com).

In a report published in May 2008 by CDS, Texas ranked number one for the total number of tornadoes from 1999 through 2007. During the time period examined by CDS the year with the most tornadoes occurring in the U.S. was 2004, in which 1,944 tornadoes were reported.

Texas leads all other states in the number of tornadoes because of its location and size. Kansas, which ranked second on CDS’ list of most tornado-prone states, leads in the number of most severe F4 and F5 tornadoes. From 1999 through 2004, Kansas had 1,616 tornadoes, 11 of them were F4 tornadoes and 9 were categorized as F5. As Arkansas, Louisiana, Texas and states throughout the Midwest can attest, 2008 is setting a pace to perhaps beat 2004 in recording the highest number of tornadoes for one year.

CDS reported that according to National Oceanic & Atmospheric Administration (NOAA) data, in an average year the U.S. experiences 1,200 tornadoes that kill 55 people, injure 1,500 and cause more than $400 million in damage.

Numbers of Tornadoes Increase

Prior to 1990, the average number of tornadoes per year in the Continental US was 772. In the period from 1990 through 2007, the average was 1,215. The number of tornadoes reported has gone up over 50 percent, according to the CDS study. “With this in mind, the number of years of data used in the model was reduced to the time period beginning January 1990 and ending December 2007,” the study said. It continued on, “Again, we believe the bias was caused by the method of reporting tornadoes. In earlier years, all reporting was probably visual, while in later years, remote sensing (primarily radar) was most likely used. Additionally, many areas that were previously raw land have probably been developed into suburban housing, thus the reports of damage have increased. ”

In the past, these tornadoes may not have been reported as they hit open farmland, causing no insured damage. If this bias was caused by changing weather patterns, then this reinforces the fact that we should use a shorter period, even if it gives us less data. We want to take into account the higher frequency of events this provides. Cutting the time period down to 1990-2007 reduces the number of tornadoes to 21,800 as opposed to 52,400 from 1950-2007.

Scale and frequency

Tornadoes are usually classified using the Fujita Tornado Scale, or FScale developed by Dr. T. Theodore Fujita at the University of Chicago in 1971, CDS said. Using FScale classifications, the study looked at whether there was any correlation between tornado strength and frequency of tornadic activity. The study found no “strong correlation between strength and frequency.”

“The areas with the most tornadoes don’t necessarily have the strongest tornadoes,” the report said. “This is true of Florida, which experiences many small tornadoes and waterspouts. In fact, although Florida is ranked third in terms of the number of tornadoes, there were no F-4 or F-5 tornadoes reported during the study period.”

Other Studies Weigh In

According to the New York-based Insurance Information Institute and A.M. Best tornadoes caused an average of $4.9 billion in property/casualty claims each year from 2001 to 2007, according to an A.M. Best study. The costliest year was 2006, with more than $8 billion in insured damages. The study foresees high tornado losses in 2008, based on first-quarter estimates, with about $850 million in insured damages from the “Super Tuesday Tornado Outbreak” in the South in early February. The study found that tornado losses are approaching those of hurricanes, with insured damages of $1 billion or more from a single event becoming more common.

Other key findings of the A.M. Best study:

On average, tornadoes and related events have accounted for nearly 57 percent of all catastrophe losses per year since 1953.

A March 31, 1973, tornado in central and northern Georgia was the costliest tornado on record, with $5.35 billion in damage in 2008 dollars, based on total damages, not just property insurance losses. The next four most costly (in 2008 dollars) occurred on June 8, 1966, in Topeka, Kan., ($1.99 billion); May 11, 1970, in Lubbock, Texas ($1.47 billion); May 3, 1999, in Oklahoma City, Okla. ($1.34 billion); and April 3, 1974, in Xenia, Ohio ($1 billion).

New Jersey tops the list of states with the highest average expected losses, followed by Connecticut, Massachusetts, Ohio and Rhode Island, based on A.M. Best’s analysis of Risk Management Solutions modeling data. Texas has the highest expected annual average occurrence rate, followed by Oklahoma, Kansas, Missouri and Nebraska.

Tornadoes can occur at any time of the year, the conditions that cause tornadoes are most common April through September.

Topics Catastrophe USA Texas Kansas AM Best Oklahoma

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