Believe it or not, spring is coming. Summer will follow, and with it will come the increase in potential for severe weather and tornadoes.
But whether Nebraska and Iowa will see more of such storms than usual this year, forecasters can't yet say. There are many factors that contribute to tornadoes that can't be predicted this far out.
“We just don't have within our grasp the ability to predict that far in advance,” said Greg Carbin, warning coordination meteorologist for the federal Storm Prediction Center in Norman, Okla.
The season so far has been a slow one. Only 43 tornadoes had been reported nationwide this year until one nicked a small town in western Oklahoma on Monday night. Typically, the country counts between 70 and 100 by early March.
Nebraska and Iowa haven't yet seen any severe weather. Forecasters here are still tied up with flood watching.
At this time of year, tornadoes typically strike along the Gulf Coast. As the weather warms to the north, so will the potential for severe weather. April, May and June typically are busier months for such storms in Nebraska and Iowa.
“If we were to get one in South Dakota now, that would be unusual,” said Adam Houston, an assistant professor in the University of Nebraska-Lincoln's geosciences department.
Not that there haven't been exceptions. The only tornado reported nationally this February occurred in California. A year ago, there were 36 tornadoes in February, including the year's deadliest, a Feb. 10 twister that killed eight in Lone Grove, Okla.
Some elements of severe weather, Houston said, are warm moist air at the surface; a relatively cold layer above; and variation in the wind speed and direction, as you go higher.
But none of those things can be predicted months in advance, he said.
Carbin said there's no evidence that the El Niņo-La Niņa climate pattern cycle affects the number of tornadoes. Some El Niņo years, in which Pacific Ocean surface temperatures are higher than usual, have seen little tornado activity, others have been very active.
In fact, the year 2008 — a benchmark for an active season — was a La Niņa year, with lower than usual Pacific temperatures. Nationally, it was the 10th deadliest since the beginning of reliable records in the mid-1950s, with more than 1,600 tornadoes. Among them were the May 25 twister that devastated Parkersburg, Iowa, killing nine. On its heels came the June 11 tornado that claimed the lives of four Boy Scouts at Iowa's Little Sioux Scout Camp.
“So we can't say, ‘El Niņo, more tornadoes,'” Carbin said. The winter of 2009-10 has been an El Niņo season.
Houston will help track tornadoes again this summer when he participates in VORTEX2, a study aimed at improving the accuracy of tornado warnings. It follows an earlier version in the mid-1990s.
Last year's relatively quiet tornado season wasn't ideal for the researchers, he said. While Houston isn't wishing for tornadoes, he hopes to put them to good use if they do come.
“For us to advance the science, we need more events than we had last summer,” he said. “We hope we will have more opportunities to get some good data.”
This report includes material from the Associated Press.
Contact the writer:
444-1223, julie.anderson@owh.com
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