120413 clark fork ice

Ice forms on the Clark Fork River in downtown Missoula recently. Subzero wind chills are expected across western Montana this week.

An arctic air mass moving into western Montana on Thursday and Friday should send temperatures to the single digits and push wind chills well below zero.

“Most people around here, if they haven’t lived up here in the last 30 years, may not have seen this before,” National Weather Service meteorologist Jeff Kitsmiller said in a conference call Tuesday. “This could be a period where we have some of the coldest average temperatures we’ve had in 40 years.”

One cold front was already getting established over the Rocky Mountains on Tuesday, which dropped the mercury from 41 on Monday to 22 on Tuesday afternoon in Missoula. The next front should be considerably harsher, Kitsmiller said.

“We could have places on Friday that don’t reach zero degrees,” Kitsmiller said. “There’s some moisture coming, but only ice crystals or very light snow.”

Starting Wednesday, daytime high temperatures will struggle to exceed 10, while nighttime lows will be well below zero. In addition, wind gusts as strong as 30 mph will make the cold even worse. Wind chill effects will make the air feel around minus 25 to minus 30 in some places along the Continental Divide and between 10 and 20 below zero in the rest of the northern Rocky Mountains.

That raises threats to schoolchildren waiting for buses, livestock looking for shelter and pets in outdoor kennels. While the arctic cold isn’t expected to make roads slippery, any motorist getting stranded with engine trouble could risk frostbite if not properly prepared for an exposed wait.

Bonner Elementary School Superintendent Doug Ardiana said teachers check the temperature and wind chill levels before any recess or lunch break, and keep children inside if the wind chill is worse than 10 below zero.

“It’s very, very rare that Bonner ever closes school or delays buses,” Ardiana said. “We feel people are prepared to act appropriately with the weather.”

However, he added that nine of 10 Bonner students ride the bus to and from school every day. Parents may want to drive their children to school or wait with them at bus stops Friday if conditions get serious.

There’s a possibility that snow could be added to the mix by Monday, but forecast models haven’t settled on that yet. The weekend cold front has most of the attention.

“By Saturday morning, we really could drop the bottom out,” Kitsmiller said. “It’s bringing some of the coldest air I’ve seen in a long time. The preparedness people have done in the past may not be enough.”

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Reporter Rob Chaney can be reached at 523-5382 or at rchaney@missoulian.com.

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