Boletín de aludes

Silver Valley & Bitterroot Mountains

Idaho Panhandle Avalanche Center
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Peligro de aludes

Mon
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Desactualizado: este boletín caducó 2 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

New snow and variable winds have built thin slabs on many slopes at upper elevations. Anomalous east-northeast winds followed by more westerly winds likely broadened slab formation to atypical slopes and start zones. Recent snowfall is heavier and denser than prior storms and avalanches may be easier to trigger on slopes where drifted slabs are around 8 inches deeper. Stick to sheltered areas and go around steeper places if you see cracking in the snow or where the snow surface looks smooth and rounded.

Problemas de aludes

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–1.5

    Over the last two days, snow totals range 4 to 7 inches in the Bitterroot Mountains - Silver Valley. The latest round of snowfall arrived with warmer air than prior storms, initially driving the rain line to around 6,500 feet before transitioning to wet, heavy snow. Having a slippery sliding surface directly below may allow these shallow slabs to be more reactive, and they could break wider than you expect where drifting is slightly deeper. Pay attention to the direction a slope faces, look for fresh cornice growth, and anticipate problematic drifts to lurk in places you aren't accustomed to seeing them after the variable winds. Use caution on slopes around 35 degrees if you notice the snow surface transition from soft to stiff or observe blowing snow along ridgelines.

    Triggering a smaller slide above a cliff or terrain trap could carry higher consequences if you don't have an exit strategy.

    (1/1/2025)

    A shallow, soft slab avalanche failing in the recent storm snow. Bitterroot Mountains. January 1, 2025.

    Photo: Izzy Davis

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    2–3

    Faceted grains persist underneath a couple of older rain crusts two to three feet deep across our forecast zones. The overlying slab has stiffened significantly in the last week and makes impacting these weaker grains more difficult. Where the crust has degraded and is more breakable, the facets are overall larger and weaker. Your chances to trigger one of these lower-probability, higher-consequence slides increase near exposed rocks or wind-scored areas of slopes where these weak snow grains may be closer to the surface.

    Persistent slab avalanches can behave unpredictably and span across adjacent terrain features. Choose slopes free of surface obstacles or terrain traps just in case something goes wrong. Default to lower-angled slopes if your snowpack assessments are inconclusive around the sensitivity of faceted crusts.

    (12/31/2024)

    The December 18 rain crust is thin, breakable, and very translucent. It lurks around two feet deep and was stubborn in our snowpack tests. We did observe resistent planar failures with moderate force. Selkirk Mountains. December 31, 2024.

    Photo: Chris Bilbrey

Avalanche Discussion

Two-day snow totals have landed slightly less than the models initially thought. None-the-less, all mountain regions received enough new snow to refresh surface conditions but not enough to significantly raise the avalanche danger. You can still find trouble and more concerning hazards will likely be confined to the recent storm snow. Monitor how much new snow has fallen as you travel across aspects and up in elevation. The latest storm blessed us with a variety of wind directions so anticipate more cohesive slab formation on slopes that normally harbor shallower slabs or are usually wind scoured.

The main question to ponder before committing to steeper slopes is whether a shallow avalanche you trigger stays confined to the recent storm snow, or breaks deeper into a faceted crust? As we move further away from a significant loading event, this step-down scenario becomes less likely. Knowing exactly how close these grains sit to the “reactive” edge is a big unknown. This uncertainty can best be managed through conservative terrain choices. Avoid likely trigger spots or lingering below a slope while other group members or another group ascends or descends. Have a solid exit plan, only expose one person to a slope at a time and realize deeper breaking avalanche may provide no warning signs prior to failure.

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On Thursday in the Bitterroot Mountains, the forecast staff spotted the first glide crack of the season on an east-facing slope around 6,300 feet. This crack is on the same slope where a crack opened last season, then failed naturally producing a size 3 slide. While this seems like an anomalous event at this point in the season, be mindful of how close you get to them and avoid traveling on or below any slope where you see a glide crack.

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