Bulletin d’avalanche

Silver Valley & Bitterroot Mountains

Idaho Panhandle Avalanche Center
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Danger d’avalanche

Wed
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

Snowfall and wind since late Sunday have created new avalanche problems that may be challenging to avoid. You’re likely to trigger storm slabs in our 6-10” of new snow which fell on several potential weak layers. Wind slabs on lee slopes above treeline will be larger and also likely to produce human triggered avalanches. Except for wind scoured areas you will be hard-pressed to find avalanche terrain without one of these two avalanche problems. Temperatures in the teens today and dropping below 0F tonight might further motivate you to choose low consequence terrain. Excellent riding conditions can be found on low angle terrain.

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–1.5

    Storm slabs that are somewhat small, though still large enough to ruin your day or worse, are truly touchy where they rest on large, buried surface hoar. These “slabs” are soft and barely cohesive, making it difficult to produce reliable results from our typical stability tests. Instead focus on red flag information like cracking under your feet or machine, whumphing, our 6-10” of recent snowfall, and at least some recent avalanche activity. Know that we were able to remotely trigger one such avalanche yesterday on a relatively mellow, 30-degree slope.

    We expect greatest sensitivity in open areas near and below treeline, which is where you’ll likely find the largest buried surface hoar and where the wind may have added a little cohesion to our storm slab. There are also areas of near surface facets below the new snow, and some of our most sun exposed aspects have these persistent weak layers sitting on a smooth sun crust. Though fairly widespread in open areas and sparse trees, these weak layers still vary significantly on otherwise similar slopes. Some will provide instant feedback like cracking or whumphing, some will provide minimal feedback but still be capable of avalanching, and some might be stable. We’ll likely all be tiptoeing around in the mountains for a while as we watch for what these persistent weak layers produce.

    (1/31/2022)

    Visible surface hoar in the crown of this avalanche, a soft slab remotely triggered on a 30 degree slope, NE aspect, 6000'. Lookout Pass area.

    SS-ASr-R3-D1.5-I

    Photo: Ryan Matz

  • Wind Slabs

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

    Sustained moderate to strong winds, blowing from the W and SW, have built large new wind slabs on the lee side of exposed ridges and cross loaded other terrain. These deep drifts of new snow will be at least a little firmer than our otherwise soft storm snow and you can avoid them by choosing the wind scoured side of terrain features or staying in lower elevation, wind sheltered terrain.

Avalanche Discussion

New instabilities that we expect to linger for a while are a stark contrast to our recently stable snowpack. On the bright side, though, we have limited concern for deeper weak layers. There are some facets around the January 12th crust where it’s thin at upper elevations, but avalanches are unlikely to step down to this layer at the present time.

Our wind slabs will gain some stability over the next few days, but we should all be thinking about our now-buried surface hoar for the foreseeable future. Our shallow storm slabs will become persistent slabs and likely become larger with more snow later this week. Areas that seem stable now may “wake up” with additional loading in the future. Conservative terrain choices are wise as we all observe how this spatially variable weak layer reacts to current and future snow load. Remember that avalanches on persistent weak layers can initiate on relatively low angle slopes, as mellow as 25 degrees in extreme cases. Enjoy the good low angle riding and sliding and please submit an observation in relation to any of our new avalanche problems!

Régions couvertes