Drought results in fewer tornadoes

Friday, August 24, 2012 | 9:07 p.m. CDT

COLUMBIA — There is at least one happy consequence to the hot, dry weather that has parched Missouri and much of the country's midsection.

Fewer tornadoes.

Only 24 have been reported in the state since Jan. 1, said Jayson Gosselin with the National Weather Service Forecast Office in St. Louis.

Compare that to the 97 tornadoes that landed in 2011. Of those, a “very small number” occurred after August, Gosselin said.

Pat Guinan, climatology professor at MU, used one word to explain the difference: "drought."

Seventy percent of Missouri’s tornadoes occur between March and June, Guinan said.

Often warm, dry winters, such as the one in 2011-2012, lead to drought conditions in the summer. The result is often a relatively tornado-free stretch.

“(Two winters ago) was a colder winter," said MU meteorology professor Anthony Lupo.

"We had more snow, more moisture in the Midwest. As winter retreated, and the warmer air came in, it provided that contrast that you need (for a tornado to develop).”

When the moist air from the south and the cool, dry air from the north converge, that instability can create thunderstorms, Lupo said.

“If you get severe thunderstorms, it’s always possible to get tornadoes.”

After the wet winter of 2011, a total of 1,625 tornadoes swept across the country, the National Climatic Data Center reported.

The storms killed 551 people, the most in 62 years of record keeping.

Of those, 158 died in the May 22 Joplin tornado, deadliest in U.S. history since 1950.

Most of southern and western Missouri has dealt with "exceptional" drought this summer, which is even drier than "extreme" drought.

Since May 1, the Columbia area has received just 4.71 inches of rain — 12.19 inches less than the yearly average and the smallest number ever recorded by the National Weather Service.

In an effort to aid affected farmers, U.S. Secretary of Agriculture Tom Vilsack recently declared all 114 Missouri counties as “primary natural disaster areas” due to the lack of rain.

With that may come a small, if guarded, measure of confidence about tornado activity, but Guinan said to be judicious about optimism.

“You just need the right conditions over one 24 hour period (for a tornado outbreak)."

Supervising Editor is Jeanne Abbott.

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