Old man winter appears ready to settle in for a bit of a stay in the Bitterroot Valley.
“It looks very wintry for at least a week or maybe the next 10 days,” said Missoula-based National Weather Service meteorologist Dan Zumpfe Tuesday. “There is lots of arctic air over western Montana and, at the same time, we’re getting a lot of Pacific moisture that is putting down snow everywhere.”
While the air feels brisk enough here in Ravalli County, Zumpfe said it’s much worse east of the divide where wind chills are predicted to drop well below zero this week.
“Wind is not going to be the biggest issue in the Bitterroot,” he said. “Cold air will be issue. It will be 10 to 15 degrees below normal each day over the next week and probably longer.”
While it’s not unusual to see a blast of arctic air slip down from the north during the winter months, this season it has taken its time to arrive.
Normally, those first arctic blasts arrive between Thanksgiving and Christmas. But up until now, this winter has, at times, almost been balmy.
“These cold air outbreaks (the term meteorologists prefer instead of polar vortex) happen every winter from time to time,” Zumpfe said. “This winter it’s been late to arrive … We really haven’t had one down in the Bitterroot until now.
“The timing probably is the most noteworthy thing about this cold air outbreak,” he said. “It’s a little backwards. It reminds me of last year when we had another pretty significant cold air outbreak at the end of February.”
Last week’s wind and snow event will probably replay Friday and Saturday, although Zumpfe said there probably won’t be quite as much snow in this second bout.
“There will probably be one to three inches of snow in most of the Bitterroot Valley,” he said. “Mountains could see three to six inches.”
It will be a little bit colder too. On Sunday morning, the projected temperatures will drop to one below zero in Stevensville.
This cold weather combined with plenty of moisture from the west has helped bump the Bitterroot snowpack up into the normal range for this time of year, said Bitterroot National Forest hydrologist Andy Efta.
Before last weekend’s storm, the snowpack in the Bitterroot basin was running somewhere between 70 and 80 percent of normal.
“Things have bumped up since then,” Efta said. “We are in pretty good shape right now in the basin.”
The amount of water stored in the snowpack in the Bitterroot Tuesday was at 90 percent of the 30-year median. And the amount of water that’s dropped into the basin since October is 95 percent for that same time period.
The far southern reaches of Ravalli County continue to trail the rest of the valley.
Efta said the snowpack depth in the West Fork and Lost Trail is about 80 percent of normal. Elsewhere in the valley it is at about 100 percent.
People venturing out into the backcountry need to aware of potential avalanche conditions.
“My guess is it’s going to need a little bit of time to settle,” Efta said. “There was a pretty good crust on the snow before this last snowfall. Based on what I’ve seen, it will take some time for that to bind up.”
The Missoula Avalanche Center said Tuesday that there was moderate avalanche danger in the West Central Montana backcountry, which means that human triggered avalanches are possible with a potential for large avalanches in isolated areas.
To learn more, visit www.missoulaavalanche.org