Minnesota's 2012 tornado season will go into the books as one of the less eventful ones.
It's all but certain the final tally for the year will be 33 tornadoes -- all of them low-level EF0 or EF1s, said National Weather Service warning coordination meteorologist Todd Krause.
The annual average since 1950 is 27, but Krause noted it's closer to 40 for the last 20 years, in part because more watchers are reporting more tornadoes. Two years ago Minnesota led the nation with 113. Last year there were only 31.
Krause noted that the warm spring seemed to have lit the fuse on an explosive season. A twister in Elysian, Minn., on March 19 was the second-earliest on record (by a day), and by May 5 there had been 23.But the midsummer months were quiet, although a a water spout that danced off Lake Superior on to Duluth's Park Point Aug. 9 was classified as a tornado.
Tornadoes are a warm-season phenomenon, but Krause said this summer was in some ways too warm. Air was so warm at higher elevations that the warm ground-level air didn't rise as quickly as it would have into cooler air, which would normally trigger strong air movements, including rotation.
Nationally, 996 tornadoes have been reported through Thursday, though that number will be revised by tornado investigators in coming weeks. The recent average through September is 1,243.