2.) Amarillo, Texas

3.) Oklahoma City, Okla.

4.) Wichita, Kan.

5.) Dallas/Fort Worth, Texas

6.) Arlington, Texas

7.) Denver, Colo.

8.) Colorado Springs, Colo.

9.) Shreveport, La.

10.) Kansas City, Mo.

The firm noted that hailstorms are a continuing threat to property-casualty insurers, with more than 13,000 hail storms in the United States in 2005 alone.

CDS said that according to Swiss Reinsurance, four out of the top-20 most costly insurance losses of 2005 were hail related.

The company said that although data was available from 1950, it only used the data from 1990 forward because it believes that in earlier years, hail storms were under-reported.

"We're guessing that the methodology was changed from visually reporting to remote sensing (radar or the like)," CDS said in an earlier report on tornadoes.

According to CDS, in virtually all years prior to 1990, the number of hail storms was significantly lower than in later years. In the years prior to 1990, the average number of hail storms per year in the United States was 1,363. After 1989, the average number of hail storms per year was 10,238.

The mapping firm said this reporting bias is also present with its tornado model, but to a lesser extent. Prior to 1990, the average number of tornadoes per year in the United States was 772. In the period of 1990 until the present, the average was 1,424.

With this in mind, CDS said the number of years of data used in its model was reduced to the time period beginning January 1990 and ending December 2005.

It said this was also done so that the hail and tornado models use the same time period.

More information about the frequency and geography of hail is available by contacting Daniel Munson, CDS vice president of sales and marketing, at 617-737-4444 or [email protected].