Drought has meant fewer tornadoes in 2012
08/22/2012 4:17 AM
02/21/2013 2:20 PM
If it’s at all possible to put a positive spin on a searing drought that has withered crops, dried lakes and altogether fried a weary Heartland this summer, it may be this:
Preliminary data gathered by scientists at the National Oceanic and Atmospheric Administration show that fewer tornadoes skipped, dragged or plowed across the United States in July than during any other July in the 60 years since reliable numbers began being recorded. The same analysis shows that the summer of 2012 may break the record for the fewest tornadoes for any U.S. summer.
In prime tornado season, from mid-April to late July, the U.S. typically sees about 850 twisters — two-thirds of the 1,300 or so that sweep across the nation yearly.
“This year, we are going to end up with about just a little less than 300 (in the height of the season), more than 500 tornadoes behind what would be normal,” said Harold Brooks, a research meteorologist at the National Severe Storms Laboratory in Norman, Okla., who analyzed the data with colleague Greg Carbin, a meteorologist at NOAA’s Storm Prediction Center, also in Norman.
August, with about 20 tornadoes reported so far, tends to be one of the least active tornado months, ranking fourth behind December, January and February.
The number of July twister touchdowns this year was a skimpy 12 — a far cry from the 150 or so that have been known to rake across the lower 48 states in the late summer months. Before this year, the quietest July was in 1960 when 42 tornadoes swept across parts of the U.S.
Brooks said the reason is as clear as the omnipresent pale blue skies overhead: No thunderstorms.
“You need to have thunderstorms as a starting point, and that hasn’t happened,” he said. “We’re all aware of that.”
Wind shear is also vital. That, too, has been sorely lacking with the jet stream and its attendant winds coursing up into Canada. Those currents are ranging farther north than is typical and compounding the drought.
“As the summer progressed, the drought just got deeper, more intense,” said Jim Keeney, weather program manager for the National Weather Service Central Region Headquarters in Kansas City. “There was no chance to develop the storm systems that produce any kind of precipitation, let alone tornadoes.”
Likewise, the more northerly flowing jet stream also pushed lower-48 storm chasers — accustomed to stalking violent vortices through the Tornado Alley that runs from Texas through Oklahoma and Kansas — into the northern climes.
“It’s been really slow for those people as well,” Keeney said. “A lot of them had to go way farther north and had to move up to Canada.”
To be fully accurate, Brooks and Carbin looked at the numbers while trying to adjust for tornado “inflation” — the fact that better technology, along with more storm chasers and spotters, would likely provide more accurate tornado numbers than in past years. In other words, historical tornado numbers are probably far less than actually occurred.
Adjusted for inflation, the 42 tornadoes that occurred in July 1960 would be adjusted up to about 73, making the paltry 12 of the most recent July even more significant.
Last year, by contrast, saw 1,691 tornadoes reported across the country. Only 2004, when the country was hit by 1,817 twisters, had more on record.
The great tornado “drought” of 2012 becomes notable considering the year’s violent start, with far more tornadoes than average recorded in January, February and March.
“We were about 100 tornadoes above normal through March,” Brooks said.
Then, on April 14, 80 tornadoes walloped the nation in a single day, with 12 spinning through parts of Kansas, including on the edge of Wichita, where a mobile home park was splintered by raging winds.
This year is no gauge of next year’s tornado season, Brooks said. What is certain, Keeney said, is that one of the droughts is going to continue for the time being.
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