Temperature change helps raise avalanche danger
"Travel in avalanche terrain is not recommended."
With drastic warming settling over Northwest Montana, that was the basic message Tuesday from the Glacier Country Avalanche Center.
The official avalanche danger across the region was rated "high" until the next hazard analysis, which will be issued Friday.
"Because of rapidly warming temperatures and precipitation in the form of wet, heavy snowfall or rain, unstable wet slab layers and loose snow are likely on steep slopes on all aspects in all of the mountainous areas of Northwestern Montana," the advisory states. "Both natural and human-triggered avalanches are likely, particularly on large, steep, smooth, open slopes and gullies."
Temperatures that had been near zero a day earlier climbed to the mid- and upper 30s Monday night and Tuesday morning.
The sudden temperature change, along with half an inch to an inch of precipitation falling over a 12-hour period, caused the sudden shift in snow conditions. It also caused hazardous conditions on roads.
A mid-January warming seems to happen every year, said Stan Bones, a Forest Service avalanche specialist.
"If you look at the climate record, this is very typical. We used to refer to this as the January thaw," he said. "There is this normal trend where you have this cold weather in early January followed by a dramatic warming … It shows up graphically on the 30-year Snotel record."
The long-term record also shows that more cold weather usually returns, creating a more settled and reliable snowpack, Bones said.
"This is really kind of a settling event that lets the snowpack consolidate so there's not bottomless powder for the rest of the winter," he said. "The snowpack takes on a lot of strength and stability after this. It becomes a strengthening event once it refreezes."
In the meantime, however, Bones reiterated that avalanche danger is currently high.
"I'm sure there's been some avalanches out there," he said.
What's different this year, he said, is that this year's snowpack is visibly below average in the mountains.
The Natural Resources Conservation Service reports that mountain snowpack is 74 percent of average above the Kootenai River Basin and 73 percent of average above the Flathead River Basin, but Bones said those figures are largely based on precipitation that fell and melted in early winter.
"The snow depth, it's just not there," said Bones, who tests snow conditions in the field twice a week. "The startling thing to me is there's just not a lot of depth to it. There's brush fields all over the place."
And those conditions can reduce the potential for avalanches because snow can be supported by "a lot of vegetative and terrain anchors."
A small avalanche broke loose several miles east of West Glacier early Tuesday morning, temporarily blocking U.S. 2, said Steve Herzog, the Montana Department of Transportation's Kalispell area maintenance engineer.
"It was over the road and closed it for a short period of time," Herzog said. "It took us about 15 minutes to clean up."
The slide was about 4 feet deep and occurred around 1 a.m. as heavy snow and freezing rain fell across the region.
Reporter Jim Mann may be reached at 758-4407 or by e-mail at jmann@dailyinterlake.com