More rain, maybe tornadoes, to come

BATON ROUGE, La. — Currently, there's a very large, cyclonic weather system stationed over the Midwest, says Barry Keim, regional climatologist at the Southern Regional Climate Center in Baton Rouge. Keim says this system is the impetus for the storms experienced in the Midwest on May 4. The system will also increase opportunities for storms in the Delta during the week of May 5 — particularly in Arkansas, Missouri and Tennessee.

"But while there's always potential for more storms — there's a cold front that will sweep through over the next 36 hours — from what I'm seeing it doesn't appear the system is generating many thunderstorms yet. My suspicion is the next couple of days won't see the same intense storms that were seen yesterday," says Keim, who spoke to Delta Farm Press on May 5.

Having said that, "this is prime time for tornadic activity in this part of the country. For the country as a whole, the months of April through June are by far the most active for tornadoes to form."

As we come out of the winter season, the upper part of the atmosphere remains chilled. As spring arrives, the surface heats up but the warmth lags in the atmosphere's higher elevations, says Keim.

"That means it feels warm on the surface, but high above the temperatures are still cold. That dramatic difference in temperatures creates an environment that's highly conducive to tornadic activity."

The United States — actually the Great Plains — gets more tornadoes than any other country in the world. In fact, the United States has more "by far — and I can't emphasize the 'by far' enough. We're the runaway tornado winner."

The reason for such an abundance of tornadoes has to do with the orientation of North American mountain ranges.

"There is a big spine — the Rocky Mountains — to the west of the Great Plains. But the plains are relatively flat practically all the way to the North Pole and Siberia."

Cold, dry air spills out of northern Canada and moves swiftly to the Great Plains with hardly any obstacle, says Keim. That air meets up with warm, moist conditions blown in from the Gulf of Mexico. The two highly opposing air masses meet for battle at ground zero: usually Oklahoma, which has the highest incidence of tornadoes.

"As those two masses collide, the frontal boundaries are where tornadoes form," says Keim.

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