Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

At upper elections in the Bitterroot, it is possible to trigger a wind slab. Below ridgeline, the snowpack is mostly stable. Stay alert for signs of instability, such as shooting cracks, and avoid steep wind loaded start zones at upper elevations. At Gash and the surrounding drainages, there is a possibility of large persistent slab avalanches up to three feet in depth. Avoid slopes over 35º in this area. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3

    A crust-facet combo is buried up to 3 feet deep in the Gash area. 

    There are multiple crowns from natural avalanches that likely failed on this layer in the Bear Creek drainage. These probably released between last Thursday's wind event and Sunday’s storm. 

    The extended column test continues to show a high likelihood of propagation at Gash. 

    This layer is most likely found between 6500’ and 7500’. All aspects are suspect. 

    Persistent layers like this can remain a problem for extended periods and will likely not give warning signs before failing. 

    The extended column test can be used for assessment. However, it can sometimes produce false stable results on such layers. The Propagation Saw Test can help in the assessment. 

    If you triggered a slide on this layer, it would be large and destructive. 

    It’s best to avoid slopes over 35º and convexities at Gash and in surrounding drainages until this layer bonds further. 

  • Wind Slabs

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

    Westerly winds have increased and are transporting snow onto previously scoured east faces. East aspects have been scoured down to crusts or contain dense windboard in many places. Both of these are slick sliding surfaces for newly developing windslab. Wind slab on west aspects, deposited ealier this week, may still be reactive in isolated areas. 

    Upper elevation start zones, just below ridgelines with terrain over 35º, is the most likely place to trigger a windslab. 

    Stay alert for signs of instability such as shooting cracks and avoid pillows of wind deposited snow, especially where terrain traps such as steep gullies or cliff bands exist.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    With rising temperatures and clear skies today, loose wet avalanches are possible on solar aspects.

    These will likely be small but could knock skiers and riders off their feet or push them into terrain traps. 

    As temperatures rise throughout the day, stay alert for warming snow surfaces. If roller balls begin, start moving to shadier aspects.

     

Avalanche Discussion

The past 48 hours have continued the pattern of sub-zero nights and cold days. Temperatures were more manageable with highs of 14º at 7400’ feet yesterday. Skies have been clear, and we’ve had no new snow. Winds began to pick up out of the west yesterday, reaching 25 MPH at Point 6.  

Yesterday in the mountains, we found similar conditions to Wednesday, with the addition of increased wind transport at upper elevations. More evidence of recent avalanches was spotted in the southern and central Bitterroot and Swans. These are the isolated pockets of windslab discussed in the previous forecast. They were small but pose a problem in exposed terrain and with terrain traps. Cornices pose a problem as well, with one large cornice failure reported. Give cornices a wide berth when above and avoid spending time below. Except for wind slabs at upper elevations, conditions are mostly stable, with no layers of concern in the southern Bitterroot, Lolo Pass, the Rattlesnake or the Swan. 

The exception to the mostly stable snowpack is found at Gash and the surrounding drainages. A layer of facets buried 32” deep is propagating in tests, and multiple crowns from large avalanches are visible from the ridge. These are up to 500’ wide, down about 3 feet, likely on the same layer propagating at Gash. Deeply buried facets are hard to predict, may not give clear warning signs, and can produce false stable results in tests. It will be hard to trigger this layer at this depth. However, if you did, the avalanche would be large and destructive. We don’t yet know the layer's full distribution. It’s best to give this some time to bond before stepping into prime avalanche terrain in the Gash area and surrounding drainages. 

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Ski and ride safe

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