Midwest’s ‘worst tornado outbreak in last 10 years’

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WORTHINGTON — Wednesday morning even meteorologists were marveling at the tornadoes and storms that struck southwest Minnesota and southeast South Dakota Tuesday night.

“Apparently this is the worst tornado outbreak that at least people in this office can remember in the last 10 years of so,” said Tom Kriehn, a deputy meteorologist with the National Weather Service (NWS) in Sioux Falls, S.D.

“In 1974, we had a similar outbreak in the Midwest, but none right here for at least 10 years.”

On Wednesday, NWS officials were out assessing the damage. Kriehn said 15 to 20 tornadoes were reported Tuesday.

“It will boil down to probably between five and 10, and of the five or 10, about five will be fairly big ones,” he said. “We had a lot of straight line (wind) damage, too, and sometimes it’s not easy to tell the two apart.

The system that struck Leota, Chandler and Lake Wilson definitely was a tornado, according to Kriehn.

Tornadoes generally follow a path that is “so wide and so long,” Kriehn said. Damage from straight-line winds usually is spread out over a wider area.

Kriehn described Tuesday night’s vicious weather as a “very well-organized storm system.” It was spotted in advance and could be tracked, much like a winter storm, he said.

Super cells are a special breed of thunderstorms that are long-lived and hang together for a long time, Kriehn said. That is what struck southwest Minnesota Tuesday night.

“Most thunderstorms have an average lifespan of 20 to 45 minutes and they dissipate,” he said. That is what struck the area Monday night, a series of thunderstorms that dissipated and were replaced by others.

Tuesday night was a super cell that lasted up to six hours.

“We tracked one through South Dakota for five or six hours,” Kriehn said. “That produced tornadoes through Mitchell and Arlington. The one that moved through Chandler was a super cell also. Its track was not as long, but damage at least appears to be worse.

Tuesday’s weather was perfect for super cell development, the meteorologist said. The cell contained a high level of moisture accompanied by east and southwest winds.