Skiers and snowmobilers: Extreme avalanche danger advisory issued

Travis Craft found extremely unstable snow conditions in the Rattlesnake Mountains on Friday. (missoulaavalanche.org)

By Sherry Devlin/Missoula Current

The West Central Montana Avalanche Center issued an “extreme/high” avalanche danger warning Saturday morning for the Rattlesnake Mountains, the Bitterroots from Lost Trail Pass north to Hoodoo Pass, and the southern Swan and Mission ranges.

“Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential today,” said Travis Craft, the avalanche center’s director. “Human-triggered avalanches are likely.”

Craft and assistant director Logan King traveled into the Rattlesnake Mountains Friday, noting the snowpack structure there is weaker than anywhere else in the advisory area.

Wind-loaded slopes were prevalent in the Rattlesnake Mountains during Friday’s observation. (missoulaavalanche.org)

“The primary avalanche problem is wind slabs,” Craft said. “The winds are transporting the new snow and loading leeward slopes. We observed some slopes that were cross-loaded in the Rattlesnake.”

An observer in the southern Bitterroot also found ridges there with significant wind slabs, and John Lehrman at Downing Mountain Lodge reported new loading and wind slab development between 6,000 feet and 7,000 feet.

The National Weather Service reported mountain temperatures ranging from 23 degrees to 33 degrees across the region, with windy conditions. Point Six in the northern Rattlesnake Mountains had 20 mph winds, with gusts to 37 mph from the west.

In the past 24 hours, several inches of snow fell across the area at all elevations.

“Avoid all wind loaded terrain,” Craft advised backcountry skiers and snowmobilers Saturday morning.

Craft said the secondary concern is “persistent slabs.”

Travis Craft and Logan King found cross-loading on slopes in the Rattlesnakes. (missoulaavalanche.org)

“There are multiple weak layers in our snowpacks,” he said. “Dig a pit today to assess any weak layers before committing to avalanche terrain. Pay attention to any bullseye data (shootig cracks, collapse noises and any recent avalanche activity). These are clear signs of instability in our snowpack.”

Lastly, Craft warned of “storm slabs” created by the newly fallen, wet and heavy snow. “It will take time to bond to the snow surfaces,” he cautioned.

More wind and snow are expected Saturday throughout the region, further increasing the already extreme avalanche danger.

“Pay close attention to changing weather and snow conditions,” Craft said. “Reassess travel plans regularly today. Avoid all wind-loaded terrain. Dangerous avalanche conditions exist.”

Craft’s next advisory will be issued on Tuesday, online at missoulaavalanche.org.