Denver, Florida Cities Are Top Tornado Danger Zones

Jul 8, 2008

National Underwriter–July 8, 2008


A hazard mapping firm said today that its top 10 list of tornado-prone metro areas has five Florida cities on it, with a rural section of Denver in first place.

Boston-based CDS Business Mapping, LLC, an online hazard mapping firm, said the rankings are based on RiskMeter Online’s Tornado Model, which predicts the severity of tornadoes for any location in the Continental United States.

RiskMeter Online reported that the top ten tornado-prone metro areas are:

• A rural northeast area of Denver

• Houston

• Miami

• Hollywood, Fla.

• Tampa, Fla.

• Lincoln, Ill.

• Lakeland, Fla.

• Little Rock, Ark.

• Cape Coral, Fla.

• Oklahoma City, Okla.

CDS noted that tornado exposure has and will always be a consistent threat to insurers.

The company cited National Oceanic & Atmospheric Administration figures revealing that the United States, in an average year, experiences 1,200 tornadoes, which kill 55, injure 1,500 and cause more than $400 million in damage.

CDS said in drawing up its report that although data was available from 1950, the firm only used the data from 1990–2007. (All events from 2006 and 2007 were just added.) It used only the last 18 years, the firm said, because it believes in earlier years tornadoes were underreported.

“We’re guessing that the methodology was changed from visually reporting to remote sensing (i.e. radar or the like). In virtually all years prior to 1990, the number of tornadoes was significantly lower,” CDS said, noting that reported tornadoes have increase 50 percent since 1989.

CDS mentioned also that 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, CDS said.

According to the report, if this bias was caused by changing weather patterns, then this reinforces the fact that a shorter period should be used, even if it gives less data. “We want to take into account the higher frequency of events this provides,” the firm said.

The company said although data was available for Alaska and Hawaii, these were not used in its frequency model. Both states have had very few tornadoes, and due to the vastness of Alaska, this would have biased the model significantly.

A very high percentage of the country has very low scores. In fact, 30 percent of the country has a score of zero, meaning there were no tornadoes in the area, CDS said.

The company explained this is largely because tornadoes are phenomena that happen mostly east of the Rocky Mountains, due to weather patterns.

CDS concluded that the areas with the most tornadoes don’t necessarily have the strongest tornadoes, and while most strong tornadoes occurred in the Midwest, it was not the area of highest frequency.

Florida , which is ranked third in terms of the number of tornadoes with many small twisters and waterspouts, it was noted, had no tornadoes that measured at the top of the Fujita scale with winds above 206 mph.

CDS’ report said the highest number of tornadoes occurs in May and the least amount in December.

A free copy of the RiskMeter Tornado report is available from Daniel Munson, sales and marketing vice president, at 617-737-4444 or

The RiskMeter is used by underwriters and agents to automate property lookups. It utilizes Internet mapping technology to enable underwriters to determine the proximity to natural hazards for any property in the Unites States.

Risk Meter lookups include distance to coast, windpool eligibility, rating territories (company specific), proximity to brush, earthquake information, flood zones and others.

CDS Business Mapping, LLC offers mapping software, data and applications for insurers. The company specializes in natural hazard risk assessment tools and data.