Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

The avalanche danger will rise to considerable at upper elevations by the afternoon as a storm impacts the region with strong southwest winds. Skiers and riders are likely to trigger fresh, growing wind slabs on north and east aspects at upper elevations today. Storm slabs large enough to bury you are possible in wind-protected areas. Stay alert for signs of instability like recent avalanches and shooting cracks, and steer clear of steep, wind loaded terrain and convexities. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Fresh wind slabs will grow today as a storm impacts the region with strong southwest winds. We can expect 6 to 12 inches of snow to fall today, which is falling on another 6 to 12 inches that fell in the last 48 hours. The strong southwest winds will drift the snow into sensitive wind slabs on north and east aspects at upper elevations. Skiers and riders are likely to trigger these wind slabs today. 

    Wind slabs appear smooth and rounded and are often found just below ridges and in cross-loaded gullies. Cornices, wind lips, and drifts all indicate wind direction and loading. Signs of instability like recent avalanches and shooting cracks warn you to stay off steep slopes. The best way to mitigate this problem is to avoid wind-loaded slopes over 33º.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    With 6 to 12 inches of recent snow and another 6 to 12 inches forecast for today, storm slabs up to two feet deep are possible in areas sheltered from the wind. Pay attention to the new snow density today and watch for signs of instability, such as shooting cracks. If slabs are consolidating, stick to slopes under 35º and avoid convex rolls. 

    If the snow doesn’t consolidate into storm slabs, skiers and riders could trigger dry loose avalanches in steep wind-protected areas. While mostly inconsequential, dry loose avalanches can push riders into and over hazards. Today’s are capable of burying a person if encountered in a terrain trap such as a gully that funnels debris and increases the depth. Manage dry loose avalanches by getting out of their way and letting them run.

Avalanche Discussion

A vigorous cold front will impact the region today, bringing strong southwest winds and heavy snowfall. Dangerous avalanche conditions will develop. Southwest wind gusts are forecast to reach 40 to 50 mph during the cold front passage late this morning into the afternoon. The storm will favor the Bitterroot with up to a foot of new snow by this evening. The Rattlesnake and Seeley Lake zones are forecast to receive 5 to 7 inches of snow by this evening. Snow showers will continue tonight into tomorrow. 

Yesterday observers found 6 to 12 inches of recent snowfall with generally light winds. Dry loose avalanches and isolated soft storm slabs were the primary hazards. That will change today as strong winds drift snow into stiffer slabs. Stay alert for fresh wind slabs and the possibility of storm slabs in wind-protected areas as well. 

The recent snowfall rests on a variety of surfaces, including thin sun crusts and near surface facets, which could make conditions more sensitive today. Take a step back and give the snow time to settle this weekend. Enjoy great riding conditions on lower angled slopes sheltered from the wind. 

With the high sun angle this time of year, it doesn’t take much time for fresh snow to heat up in the sun. If the sun comes out on Sunday or Monday, look out for wet loose avalanches in the new snow on sunny aspects. If the snow is wet and rollerballs start, it's a sign to move to lower angle slopes or shadier aspects. 

Earlier this week, we received reports of a very large avalanche in the Northern Beaverhead Mountains, south of our forecast area, on an upper elevation north aspect. It failed at the ground and created a totally new avalanche path destroying tens of acres of mature timber. It likely failed naturally due to new snow and wind loading. Today’s snow and wind loading could be enough to tip the balance on similar slopes. 

The snowpack in the Northern Beaverhead Mountains is generally thinner, with a poorer structure and more persistent weak layers than in our forecast area. However, the snowpack in the Southern Bitterroot shares some of these characteristics. If you are heading out in the Southern Bitterroot or areas further south into Idaho, stay alert for the potential for deeper and more dangerous instabilities. Digging snowpits can help identify problematic buried weak layers, but stability tests may be unreliable in assessing their sensitivity. 

Please let us know what you find out there today by submitting an observation. 

Ski and ride safe.

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