HELENA – Tornadoes in Montana this year have been more frequent and more powerful than at any point over the past decade, as evidenced by twisters that destroyed an arena in Billings and killed two people in the state’s northeastern corner.
While an unusually wet spring and early summer helped extend this year’s storm season, meteorologists can’t pinpoint just what’s caused the spike.
Montana averages seven tornadoes a year, which ties it with New York for the nation’s 19th-lowest average. But over the first seven months of 2010, there were 24 tornadoes recorded in the state, according to data provided by the National Weather Service.
The weather service has been unable to find another year with as many tornadoes reported, said Dan Borsum, senior meteorologist in Billings. The year that comes closest over the last decade is 2002, when 11 twisters were recorded.
A contributing factor may be the unusually high amount of rainfall this year.
“The amount of moisture that we’ve had is allowing us to stay in a thunderstorm pattern much later in the year, and that’s allowing us to have more intense storms,” Borsum said.
But don’t blame global warming, at least not until more data is available from over a longer period that would suggest this year is something other than an aberration, said weather service meteorologist Tanja Fransen.
“You can’t say that this is attributable to climate change,” Fransen said.
In addition to more twisters touching down, the tornadoes this year have been more powerful.
The number of strong tornadoes – those rated between EF2 and EF5 on the Enhanced Fujita scale – hitting Montana averages one each year. That number has more than tripled this year just in June and July.
The tornado that killed two people and injured a third in northeastern Montana’s Sheridan County on July 26 was one of the most powerful the state has ever seen. With winds of 150 mph, it was only the fourth in the state’s recorded history to rate an EF3 on the Enhanced Fujita scale, and the first since 1988.
That tornado traveled overland for 18 miles, demolishing a bridge and an abandoned farmhouse. Then it hit the Smith ranch, an isolated house and buildings where Barbara Smith, 71, lived with her 10-year-old grandson, Robby Richardson, and her nephew, 46-year-old Steven Smith.
The twister ripped the house from its foundation and demolished everything on the property, obliterating a mobile home, blowing away grain bins and tossing vehicles more than a quarter of a mile. Cattle were found more than a mile away.
Smith’s grandson and nephew were killed in the storm. Neighbors and authorities dug Smith from her basement and transported her to a hospital in Billings, where she was listed in fair condition, a hospital spokeswoman said.
That tornado came just a month after a tornado with an EF2 rating – with winds up to 120 mph – touched down on top of the Rimrock Auto Arena in Billings, the state’s largest indoor arena.
Borsun said that once the state stops seeing so many rainstorms, and the ground starts drying out, the chances of a tornado forming will lessen.