Lawinenlagebericht

Bitterroot

West Central Montana Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
Open full map
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Kernpunkte

Human triggered avalanches will be likely today in wind loaded terrain. Larger avalanches 3-5 feet deep are possible in areas with buried surface hoar or weak snow around crusts.

Wind slabs can be identified by their smooth, pillow like appearance or by shooting cracks around your skis/sled. 

You may not see any red flags like collapsing or cracking before triggering a larger persistent slab avalanche.

If you want to avoid avalanches today, stick to slopes less than 30 degrees in slope angle and be aware what avalanche terrain is above you at all times. 

Avalanche forecasts will be issued Saturday and Sunday. A general information product will be issued Monday to cover the Monday-Friday period. Additional forecasts will be issued anytime an Avalanche Warning is issued. We are hoping to begin forecasting for the Seeley zone next week. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    3-5 feet of snow sits on top of buried surface hoar, buried near surface facets, and buried crust/facet combinations.

    • The surface hoar is the most concerning of all the weak layers. Take some time to understand surface hoar formation to better assess where buried surface hoar is possible. 
    • Areas with a thin or breakable crust with facets below is the second concern. This problem has more uncertainty than the surface hoar on how reactive it will be producing avalanches. 
    • The buried near surface facets have shown the best bonding with the new snow and the least reactivity in tests but are still suspect. 

    Expect to find these problems overlapping, or for test results to show variability on the same weak layer depending on slab thickness. Slab thickness and cohesiveness above the weak layers also has a high degree of spatial variability. 

    In short, complex avalanche conditions that are difficult to outsmart. 

    You may not see any red flags before triggering an avalanche on these layers. The best travel advice is to keep it simple. If you find weak snow below the new snow, large avalanches up to D3 in size are possible. 

    (2/3/2025)

    Widespread buried surface hoar with 2 feet or more of new snow will lead to persistent slab problems across the Bitterroot. 

    Photo: Cam Mackenzie

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Watch for fresh wind slabs along ridgelines and at upper elevation. In the past 24 hours, winds have blown from the Southeast, Southwest, Northwest, and North. Expect a complex pattern of loading on all aspects.

    The good news is that compared to the persistent slab problem, wind slabs will be easy to identify and avoid. Look for blowing snow, smooth pillow like features, or shooting cracks. 

    If you see these, stick to slopes less than 30 degrees to avoid avalanches. 

    Small wind slabs have the potential to step down and trigger a larger persistent slab avalanche. 

    (12/30/2024)

    Example of shooting cracks in a wind loaded roll. 

    Photo: Arden Feldman

Avalanche Discussion

Since the beginning of month, a series of storms has hit the forecast area putting down between 2-5 feet of snow, with the higher totals found in the central Bitterroot and along the Bitterroot crest. This new snow greatly improved skiing and riding, but is not without problems. Ahead of the storm a long period of high pressure with no new snow and cold temperatures formed an overlapping assortment of weak layers at the snow's surface that are now buried by the new snow. New snow following a prolonged period of cold high pressure is a well known avalanche danger pattern. 

The distribution of the weak layers across the mountains still has some uncertainty. Prime surface hoar growth weather was present from the 19th of January through the 27th. In addition to surface hoar, all aspects formed near surface facets at the surface. On the 28th and 29th, temperatures warmed into the low 40s with strong sun on solar aspects, forming a melt-freeze crust on top of the near surface facets, while destroying the surface hoar on solar facing slopes. 

Then we began to see snow on February 1st with light winds as the storm arrived. Since then, it's kept snowing and the SWE (snow water equivalent) totals are upwards of 3 inches of water. The new snow has been low density, but is slowly forming a more cohesive slab. On February 3, an Avalanche Warning was issued for warming temperatures and high precipitation rates with potential for this to tip us into a natural cycle. 

Visibility in the Bitterroot where we expect most avalanche activity to have occurred has not cleared up since February 1st, and we simply haven’t been able to see what slopes have slid. 

We are in a period of complex avalanche conditions with a lot of uncertainty. As the snow above weak layers becomes more slabby, we may trend into more widespread avalanches. Alternatively, we may get a day of visibility and see that most slopes already avalanched naturally, taking out the weak layers. 

The more complex and overlapping the problems are, the more it pays to keep your decision making simple. If you try to outsmart the overlapping problems, you are asking for trouble. 

Please continue to submit observations and help us keep an eye on changing conditions. Check out this video on what makes a useful observation. 

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Ski and ride safe.

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