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 that has saturated the ground 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.
Emergency officials also say there has been a comparative increase in the number of disaster assistance requests because of flooding this spring and summer. Notably, flooding on the Rocky Boy’s Indian Reservation in June led to evacuations, the closure of the reservation’s health clinic and left hundreds without drinking water. The damage was so great it resulted in a presidential disaster declaration, a relative rarity for Montana.
There also have been disaster assistance requests for flooding in Dawson, Custer, Roosevelt and Petroleum counties, said Montana Disaster and Emergency Services spokesman Tim Thennis.
“We’ve been so dry for so long, that we’ve had unseasonably heavy rainfalls that we haven’t seen for 10 years or so in some areas,” Thennis said.
But even with the increased rainfall, it’s hard to know exactly why there are so many more twisters this year. It may have something to do with the transformation from an El Nino to a La Nina weather pattern. Or it could just be bad luck.
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, weather service meteorologist Tanja Fransen in Glasgow said.
“You can’t say that this is attributable to climate change,” Fransen said.
In addition to more twisters touching down, the tornadoes hitting Montana 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 with storms reported in just in June and July.
The tornado that killed two people and injured a third in northeastern Montana’s Sheridan County last Monday night was one of the most powerful the state has ever seen and the deadliest since 1923, when a tornado killed two people in Mineral County.
With 150 mile-per-hour winds, Monday’s tornado 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 at about 30 mph, demolishing phone lines, a bridge and an abandoned farmhouse that lay in its path. Then it hit the Smith ranch, an isolated house and buildings where Barbara Smith, 71, lived with her 10-year-old grandson, Robert “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.
It was the first large tornado to hit Billings in more than a half-century, and it tore off the arena’s roof, damaged hundreds of homes and businesses and scattered debris across the city.
The next day, a series of tornadoes were reported in southwestern Powder River County, and several of those were rated EF2, Borsum said.
Not two weeks after that, another EF2-rated twister struck in the Gallatin National Forest southwest of Billings. Tornadoes in mountains are rare, particularly those that powerful, and this one left swath of downed trees 150 yards wide and a couple of miles long, Borsum said.
Borsun said substantial amounts of low-level moisture is needed for a rotating storm’s funnel to connect to the ground and form a tornado. Once the state stops seeing so many rainstorms, and the ground starts drying out, the chances of a tornado forming will lessen, he said.
But that also means the start of fire season, which could pose a new challenge for emergency officials. Authorities have worried that millions of acres of trees killed by mountain pine beetles could present an increased fire risk this year.
“We’re prepared for it if we have to deal with the fire season,” Thennis said. “Overall, I think there are a lot of resources across the northwest to help with the fire season.”
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