Bollettino valanghe

Silver Valley & Bitterroot Mountains

Idaho Panhandle Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

 Snow slabs from the past week of active weather are sitting on top of a variety of different weak layers. The most concerning snowpack recipe is where the new snow slab is sitting on top of surface hoar, which can mostly be found in sheltered areas that lack wind and sun. You can avoid problems with unstable snow by managing the slope angle by staying off of slopes over 30 degrees, staying clear of runout zones and being diligent about sticking to a thoughtful trip plan.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    A storm cycle that began on February 1st has delivered over two feet of snow in some areas of the Selkirk and West Cabinet Mountains, accumulating on a widespread mix of weak layers. Earlier in the season, the forecast advised sticking to sheltered areas for safer travel, but the mountains are keeping us on our toes—those same sheltered zones are now where snow slabs are most likely to sit atop buried surface hoar.

    Given the fragile nature of these weak layers, avalanches can be triggered from a distance and may propagate more widely than expected. Avoid the temptation to test avalanche-prone slopes over 30 degrees, even in the trees. The buried surface hoar is like a sleeping giant, ready to wake at the slightest trigger. The safest approach is to stick to low-angle terrain (under 30 degrees) and steer clear of traveling beneath steep, open slopes.

    (2/6/2025)

    One of the culprit persistent weak grains underneath the storm slab - surface hoar. Before burial, these grains were almost 20 mm in size, they have been reduced to 10 to 15 mm and well-preserved in spots. West Cabinet Mountains. February 6, 2025.

    Photo: Chris Bilbrey

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Moderate east-northeast winds, accompanied by stronger gusts, will continue to transport recent snowfall, forming unstable slabs on atypical slopes. These slabs are developing over weak layers, including  soft faceted snow crust and sun crusts. In areas near ridge lines or above tree line, watch for signs of instability, such as new or reverse cornice growth and textured snow surfaces, which indicate where fresh snow is accumulating. Triggering an avalanche in a newly formed drift or at the storm-snow interface could cause a deeper slide, increasing the risk of a larger avalanche.

    Photo: Mikey Church

Avalanche Discussion

Recent observations indicate a reactive snowpack, with natural avalanches triggered by falling cornices, snowpack tests failing or propagating easily during isolation, and avalanches being triggered from a distance due to long-running cracks. Most of these incidents are occurring on a well-preserved, upright layer of surface hoar in the north—feathers measuring 15 to 25 mm—or on a buried, weak, breakable crust in the south, both of which sit atop a foot of large, faceted grains.

Persistent weak layers tend to linger, and given their fragility (mostly F to 4F-), we’re likely facing an extended period of elevated avalanche danger. As the snowpack settles under its own weight, sensitivity to triggering may increase, or stiffening slabs may mask the lurking hazard. Snowmobilers may be at higher risk of triggering avalanches, as their machines apply greater force to deeper weak layers than skiers or riders, who tend to stay higher in the snowpack.

As you move through the mountains, evaluate not just your immediate terrain but also your proximity to steeper slopes. With a mix of buried wind-affected layers, crust, surface hoar, and faceted snow, it’s safer to avoid slopes and convex rolls steeper than 30 degrees rather than trying to outsmart the lurking danger. Triggering a large avalanche from below remains a real possibility, so avoid traveling above terrain traps like gullies or depressions where steeper hazards loom overhead—especially in areas without a fast escape route.

Key Takeaways:

  • Avalanche conditions are complex and unlikely to improve soon.
  • Stability tests should not be relied upon as definitive go/no-go indicators.
  • Avoid steep slopes and stick to terrain around 30 degrees or less.
  • Watch for red flags: fresh avalanches, cracking snow, and loud collapses.
  • The best approach today? Play it safe—enjoy the riding and skiing conditions while steering clear of high-risk terrain.

Regioni coperte