Lawinenlagebericht

Bitterroot

West Central Montana Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Avalanche danger will rise this evening with a rain on snow event at low elevation. If the storm arrives early and you find yourself in heavy rain, get out of avalanche terrain. 

Today, it will be possible to trigger a lingering wind slab at upper elevation. Look out for signs of instability, like shooting cracks and recent avalanches. 

Triggering a larger avalanche that breaks 3-5 feet deep on buried persistent weak layers remains possible. You may not see any red flags before a larger avalanche fails.

Lawinenprobleme

  • Wind Slabs

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

    Overnight winds have been strong out of the west. Many of the fetch or windward areas have developed a sun crust which will limit fresh slab development, but expect lingering wind slabs along ridgelines. These slabs are likely less reactive today, but it will still be possible to trigger. 

    Wind slabs can be identified by their smooth pillow like appearance, by shooting cracks around  your skis or snowmobile, or by a firm hollow feeling slab of snow. 

    If you find any of these, stick to slopes less than 30 degrees in slope angle.

    (2/19/2025)

    A natural wind slab avalanche that released just below a cornice on a southeast aspect at 7800 ft

    Photo: Arden Feldman

  • Persistent Slabs

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

    It remains possible to trigger a large persistent slab avalanche that fails on weak layers buried 3-5 feet deep. The persistent slab problem has been trending towards better stability, but pockets of reactive slab remain. 

    The problem has transitioned to low probability, high consequence conditions. In these conditions, there may be no red flags before a large avalanche occurs. Observations have shown intermittent propagation in tests, but don’t let that fool you into thinking there is no danger. You are more likely to trigger one of these persistent slabs in areas where the snowpack is thinner, like around rock bands or convex rollovers.  This week, forecasters found buried surface hoar and buried neaer surface facets which were producing full propagation in tests. 

    To identify the problem, you can dig down in the snow and look for poor snowpack structure with a slab above weak snow. Even if snowpit tests are unreactive, poor snowpack structure should be enough to give you pause before committing to avalanche terrain. Stick to slopes under 30 degrees in slope angle and without steep terrain overhead if you simply want to avoid the problem

    Photo: Cam Mackenzie

Avalanche Discussion

Today should be a fairly calm day in the mountains with mostly cloudy skies and a trace of new snow ahead of a larger storm arriving tonight. 

Since Monday, about a foot of snow has fallen in most areas, spread over multiple days. This snow formed some fresh wind slab at upper elevation but otherwise has not produced much avalanche danger. 

This week saw no significant avalanches. Some fresh wind and storm slabs were noted within the new snow, and yesterday, multiple wet loose avalanches ran naturally during the period of sunshine. Otherwise, observations continue to show intermittent propagation failing on the January weak layers of surface hoar, near surface facets, and crust/facet combinations. 

Expect a big change in conditions starting tonight. An atmospheric river of warm moisture is going to arrive and shake things up. The big concern is where the rain line will fall Sunday. If it rises to 6500’ like some models predict, we could see larger wet slab avalanches failing in north facing terrain which have potential to run down into areas not normally associated with avalanches. At upper elevation, dense snow and strong wind will form fresh wind and storm slabs with increasing avalanche danger. 

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

Avalanche forecasts will be issued on Saturdays and Sundays. A general information product will be issued on Mondays to cover the Monday-Friday period. Additional forecasts will be issued anytime an Avalanche Warning is issued.

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Ski and ride safe.

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