Bulletin d’avalanche

Bitterroot

West Central Montana Avalanche Center
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Danger d’avalanche

Mon
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré last year. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Natural wet loose avalanches will be likely today in areas of direct sun and at mid elevation in areas that did not freeze last night. 

If you find yourself sinking into wet unsupportable snow, or see small point releases beginning to fan out or entrain more snow, it is time to get out of avalanche terrain and move to nonsolar slopes. 

Triggering a larger persistent slab avalanche is unlikely, but specific pockets of weak snow remain in rocky terrain and on convex rollovers. You are unlikely to see any red flags before the avalanche fails unless you dig in the snow to look for weak sugary snow with a slab above.

There are small amounts of snow available for transport. Pockets of fresh wind slab at upper elevation are possible on east aspects but should be easy to identify and avoid. 

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Another day of warm temperatures and direct sun is on tap for today, with expected wet snow avalanches on sunny slopes.

    Increasing ridgetop wind speeds and high clouds should help cool the more exposed terrain, limiting the wet snow problem at upper elevation to south facing slopes. At mid elevation, the problem is more widespread as these areas will see warmer temperatures today and not as much wind.

    Avalanche size will be dictated by the size of the slope and how much wet snow can be entrained in the avalanche as it runs. Larger slopes will be capable of producing avalanches up to D2 in size. 

    The timing of the wet, loose snow will depend on how stout the melt-freeze crust is at the surface. Areas with a thicker crust will take longer to break down, whereas areas with a thin crust at the surface or no crust will become wet faster.

    By now, many slopes have already avalanched, and will be easy to identify by their debris cones. Keep in mind that multiple start zones can run into the same path, so limit your time hanging out on top of avalanche debris. 

    Wet snow is a straightforward problem to identify and avoid. If you are sinking into unsupportable wet snow, see a widespread rollerball cycle, or see small point releases beginning to fan out and entrain more snow, it is time to move to non solars slopes or slopes less than 30 degrees free of any overhead avalanche terrain. 

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3

    Triggering a larger persistent slab avalanche that fails 3-5 feet deep has become unlikely. Specific pockets of poor snowpack structure remain with buried January facets, and facet crust combinations.

    This problem still lingers in areas with rocky convex rollovers, however, even in these areas snowpit tests have become increasingly unreactive. You are unlikely to see any red flags like shooting cracks, whumphs, or feel collapsing before an avalanche occurs. 

    The trouble with looking for this problem is that you must expose yourself to the terrain most likely to produce an avalanche to dig and look for it. Digging above or adjacent to rocky rollovers will likely show a different snowpack structure than what can be found directly in the rocky rollover. If you dig in a safe area and identify weak, sugary snow with a slab above, the best bet is to stick to lower angle slopes less than 35 degrees.

Avalanche Discussion

With the spring weather comes the usual list of spring snowpack problems. Temperatures will rise into the low 40s today, but expect to see wind gusts of 25-40 mph which will make temperatures feel cooler. Today, the wind will be the determining factor on how wet the snow gets, and as a result, if and when we see a wet snow avalanche cycle. 

Mid elevations did not see a solid freeze last night, and today these areas will not be fully impacted by the wind. With that, expect avalanche danger to be highest at mid elevation today, especially in areas without a melt-freeze crust at the surface. 

With such strong winds, why no wind slab development? We don't have much snow left in our fetch areas on west aspects, as most of these areas have been stripped already, or hold a crust at the surface. If you do find a pocket of wind slab or shooting cracks, avoidance is recomended by going elsewhere or sticking to a low angle slope. 

We are beginning to see some glide cracks open. Glide avalanches are the most difficult to forecast or understand due to their unpredictability. The time between a crack opening up and the avalanche can vary from minutes to months. You are unlikely to trigger a glide avalanche as a person, but natural avalanches are possible. Avoidance is the answer. If you see open glide cracks, do not travel underneath them. 

A week of sun and warm weather has helped melt overhanging cornices back to vertical. Much of the natural cornice failure cycle has passed. If you see an overhanging cornice in direct sun or a period of warm weather, do not travel or hang out underneath it. 

 

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