This is Ian Hoyer with the avalanche forecast for Saturday, December 21st, at 7:00 am. This information is sponsored by Avalanche Alliance and Idaho State Snowmobile Association - Avalanche Fund. This forecast does not apply to operating ski areas.
This morning, there is no new snow. Winds are 10-20 mph out of the west. Temperatures are a bit above freezing in the mountains around Bozeman and Big Sky and a few degrees below freezing elsewhere.
Today, temperatures will rise into the 30s and low 40s F under partly to mostly sunny skies. Winds will remain moderate, shifting to the southwest.
Tonight, there will be a few snow showers, but only a trace-1” of new snow will accumulate.
Large Persistent Slab avalanches have been breaking on weak layers in the middle of the snowpack and near the ground (video, Henderson photo, Fisher photo). If you get onto a steep slope today, expect to trigger a similar slide. These slides can be triggered from below, so be cautious passing beneath steep slopes as well.
The first big loading event of the season only ended 48 hours ago. Persistent weak layers are widespread - these weak layers (surface hoar and facets) often remain easily triggered for a couple days after a loading event ends and we expect that to be true today.
Human triggered avalanches are likely and the avalanche danger is CONSIDERABLE. Choose slopes sheltered from the wind, less than 30 degrees steep, without steeper slopes above, for good, safe riding today.
Across the rest of our advisory area, triggering, large, dangerous avalanches is still possible, but they have become a bit less likely. The bulk of the last snowfall event had wrapped up by Monday night. High winds on Wednesday drifted lots of snow (Beehive video), but the snowpack has now had a few days break from loading.
Persistent Slab avalanches remain a serious concern. Weak layers are widespread in the middle of the snowpack and earlier this week we saw avalanches breaking on them. On Tuesday, I triggered a slide from 200 ft away on Buck Ridge (details). On Wednesday, an avalanche on Saddle Peak broke 1-3 feet deep, and ran 1500 vertical feet (photos). A large collapse yesterday in the Bridger’s reminds us that similar slides remain possible (observation).
Minimize potential consequences by choosing smaller slopes with clean runouts if you decide to get into steeper terrain today. Stay alert for signs of instability (cracking, collapsing, or poor test results).
The avalanche danger is MODERATE.
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