Which US counties are most at risk of tornado damage?

Tornado rips apart boats, power lines in South Florida

A thunderstorm produced a tornado in Fort Lauderdale on Saturday. Damage and power outages were reported from the twister, but there appeared to be no injuries, authorities said.

You may be surprised to learn that counties with major cities and high-priced real estate are some of the most at risk for tornado damage.

Chicago, Houston, Plano (Dallas Metro), St. Louis and Kansas City are all in counties that rank as the most vulnerable to damage.

File: Tornado damage in the Houston Metro area from Jan. 2023. (Brian Kelly / FOX Weather)

Gutter Gnome analysts crunched the numbers, looking at several factors:

Incidence risk: They scored counties with the highest risk of tornadoes, according to FEMA and NOAA, on a scale from 1-100. All counties scored at least 69.9. The score was weighted to account for about 42% of the ranking.
Financial risk: They scored counties based on the expected annual loss from tornadoes, according to data from the Census Bureau. This includes how dense the city is with buildings and relative costs. This accounted for about 25% of the ranking. That ranged from $1.5 million to $358 million.
Exacerbating factors: Finally, they scored counties according to the average age of homes, percentage of mobile homes and strong state building codes according to the International Code Council and the Census.

The age of the homes, between 24.5-70 years, accounted for 17% of the rank. The share of mobile homes ranged from 0.06%-42% and accounted for 12% of the final rank. State adoption of international residential building codes, ranging on a scale from 0 (no adoption) to 18 (most adoption), also accounted for 12% of the score.

Top 5 most vulnerable

Cook County, Illinois , took the top spot in the overall ranking. The Chicago Metro area had a tornado risk score of 99.97 out of 100. The average age of homes was 59.7 years, and only 0.77% were mobile homes. Illinois is tied for the lowest state adoption of residential and building codes. The annual expected loss from tornadoes is $304 million.

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File: Lightning bolt strike Chicago's Willis Tower on April 4, 2023. (Craig Shimala via Storyful / FOX Weather)

Harris County, Texas , took the second spot. The Houston Metro area scored 100 out of 100 for tornado risk. The expected annual loss came in at $354 million. The average age of homes is relatively young, at 39.2 years, with 2.6% of them mobile homes. Texas has a moderate adoption of building codes.

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File: Damage is seen in the Houston area after a tornado that swept across the eastern side of the metro on Nov. 21, 1992. (Tim Marshall/Haag Engineering / FOX Weather)

Collin County, Texas, which is northeast of Dallas, comes in No. 3. The home of Plano has a 99.94 tornado risk score and a total expected annual loss of $358 million – the most expensive. About 1.7% of homes are mobile homes, and the average age of all homes is 27.58 years.

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In the fourth spot is St. Louis, Missouri, with an average home age of 70 years – the oldest average home age on the list of over 900 counties. The state is tied for the least adoption of building codes. The county which includes St. Louis has a low share of mobile homes, 0.34% and a tornado risk of 98.6 out of 100.

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File: A highway sign sits in a parking lot at Lambert-St. Louis International Airport April 23, 2011 in St. Louis, Missouri after a tornado tore through. (Dilip Vishwanat / Getty Images)

Rounding out the top five, Jackson County, Missouri, also has a small share of mobile homes, under 1% and the average age of homes is 53.87 years. The expected annual loss for the home of Kansas City is $54.5 million with a tornado risk score of 99.59 out of 100.

YEARLY TORNADO DEATH TOLL SPIKES IN 2023 DESPITE AVERAGE SEASON

File: Salvaged items sit in front of a destroyed structure in the Carriage Hills subdivision of the Kansas City suburb of Gladstone which was the victim of a tornado on May 5, 2003. (Brendan Smialowski / Getty Images)

The US leads the world in the number of tornadoes

The U.S. averages about 1,333 tornadoes a year. Half of those usually form between April and June. The second tornado season comes in the fall. Canada comes in second with just hundreds.

Texas is by far America's most active state for tornadoes, averaging 151 twisters each year. In a distant second place is Kansas, with an annual average of 91 tornadoes. This is an area some call "Tornado Alley."

Seven of the top 10 counties with the highest total expected loss are in Texas. Gutter Gnome nicknamed the area the "Texas Triangle."

Missouri, Kansas and Illinois counties placed high on the list because the states have not yet instituted building codes that mandate things like stronger roofs, safe rooms and impact resistant windows, explained Gutter Gnome.

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