Bollettino valanghe

East Cabinet Mountains

Idaho Panhandle Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto last year. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Dangerous avalanche conditions remain as another round of heavy snowfall builds fresh slabs of snow and adds more stress to worrisome weak snow grains below. Triggering a slide in the new snow could step down into deeper weak layers producing a larger, more dangerous slide. Continue to make conservative terrain choices by sticking to slopes around 30 degrees or less,  and avoid exposure to steep, overhead hazards or traveling below large avalanche paths.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–2.5

    More wet, heavy snow is building another storm snow layer on the surface. These slabs are forming above a harder interface where rain saturated the snowpack then refroze, or onto prior snowfall at elevations above the rain line. To keep things simple, this is adding more depth of recent snow and weight to a snowpack that has shown it's true colors in the last few days. The significant hardness difference between the storm snow of the last few days to what accumulated earlier in the month is a major factor of the elevated sensitivity. Dense slabs of snow have a higher potential to break wider than you expect, even in wind-sheltered areas. If you're lucky to only observe signs of unstable snow like cracking or collapsing without triggering an avalanche, that's good fortune. Simply avoid exposing yourself or your group to steeper slopes until the new snow has a chance to catch a breath. 

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

    Prior to this weekend's storm, lingering weak layers - surface hoar, faceted grains, and a faceted crust - two to three feet deep were the culprit of the atypical, lingering instability in the upper snowpack. Snowpack tests on slopes near treeline down to about 5,000 feet continued to produce ongoing failures in these weak grains. Preserved surface hoar lingered on north to east-facing slopes, while southeast through south to west-facing slopes harbored a layer of facets or a breakable crust with facets lurking above and below. What is not known is how deep recent rainfall percolated into the snowpack and whether it made deep enough to weaken bonds in these persistent grains, or alter their change completely. The added water load to the overlying slab is enough to flex the sensitivity needle even if these grains did not see liquid water.

    (2/16/2025)

    Surface hoar feathers are still 10 to 12 mm in size below a stiffening slab. While becoming harder to impact, they still produce propagating failures in tests. Selkirk Mountains. February 16, 2025.

    Photo: Chris Bilbrey

  • Wet Slabs

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

    Rain saturated snow in the upper snowpack may keep a lingering threat to trigger a wet snow avalanche on slopes steeper than about 30 degrees. Loose snow slides that travel long distances can gouge deeper and leave a dangerous pile of snow at the bottom of a slope, or in gullies and creek bottoms. Some wet avalanches may fail as a more dangerous slab of wet snow, and those types of avalanches will be more difficult to escape. Despite the rain coming to an end, water will likely continue to percolate toward weaker interfaces or buried crusts as temperatures stay mild around 5,000 feet and lower. If you see fresh glide cracks or older ones that look wider, avoid traveling on or below those slopes.

    (4/4/2024) Photo: Mikey Church

Avalanche Discussion

From 2/24/25:

Wild weather often breeds unusual avalanche behavior. 36-hour snowfall totals around 5,000 feet and higher range 6 to 12 inches of very wet, dense snow - 17 to 25 percent snow densities. Liquid water input so far is 1 to 2 inches over the same timeframe and most elevations around 4,000 feet and lower have received all rain. Another potent slug of warm air arrives Sunday afternoon and drives the snow line higher in the sky. An above mountain top rain event will likely pan out for the Bitterroot Mountains while the highest terrain across the Northern Mountains has the best odds of being spared the major snow wetting event. 

By Monday morning, the snowpack in some places could hit the 3 to 4 inch watermark adding an insurmountable load to persistent grains that have not disappointed us in terms of their lingering sensitivity since burial on January 31. 

Storm slab densities have significantly increased from the 5–7 percent storm snow that accumulated over the past 10 days. This inverted layering makes newly formed slabs touchy, allowing avalanches to be triggered on lower-angle slopes than usual. Near and above the treeline, deeper and harder slabs can produce large, terrain-wide avalanches. Slides may travel long distances into mature forests, causing timber damage—especially if they initially fail in the upper snowpack and then step down into deeper, persistent weak layers.

Weak layers- Lingering instability in the upper snowpack comes from surface hoar, faceted grains, and a faceted crust two to three feet deep. Snowpack tests near the treeline and down to 5,000 feet continue to show failures in these weak grains. North- to east-facing slopes hold well-preserved surface hoar, while southeast- to west-facing slopes have a breakable crust with facets above and below. If prolonged rain occurs, water may penetrate deeper, reaching the January Drought Layer (JDL). If this happens, Wet Slab avalanches become a serious concern with unpredictable failure timing.

If you decide to head into the mountains today, be prepared for anything. Keep it simple and avoid pushing the limits. Avoidance is the best strategy is to steer clear of risky terrain altogether.

Regioni coperte