Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

Expect very unstable conditions in the backcountry on Monday. Avoid travel in avalanche terrain, especially at upper elevations.Choose low angled terrain well out from under and not connected to slopes steeper than 30 degrees.

Problemi valanghivi

  • Storm Slabs

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

    Another 12-18in of new snow looks to accumulate over the next 24 hours bringing snow totals since Friday up to 2-3ft+. Large natural avalanches are very likely, especially in steep wind loaded terrain near and above treeline. Fresh slabs may be easy to trigger even below treeline. Carefully assess how new snow bonds to itself and old snow surfaces. Recent observations indicate a poor bond to weak snow at the February 11 interface buried 1-2ft deep. Expect the potential for surprizing avalanches breaking widely accross terrain features. Look for red flags like shooting cracks, collapses, and recent avalanches. Avoid travel on or below slopes 30 degrees and steeper, especially convex rollovers and slopes below cornices. In areas sheltered from the wind, loose dry sluffs may run far and fast in steep terrain and could even trigger slab avalanches as they run downslope. Give the new snow time to settle and stablize and seek out simple, low angled terrain away from overhead hazard.

    (2/13/2021) A small skier triggered storm slab (D1) on a north aspect at 5400ft in Lanham Creek that failed on weak snow at the February 11 interface.

  • Deep Persistent Slabs

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

    Additional snow and wind continue to stress the snowpack, and the potential for very large deep persistent slabs remains possible. In areas above 4000ft, weak structure exists and doesn't give much confidence for the 4ft of snow resting above it. Wise backcountry travelers continue to stay well away from big, steep, and open slopes near and above treeline. Put a large buffer of terrain between where you travel and large avalanche paths, especially wind loaded areas. Travel like the slopes could avalanche big, and make sure to stop and regroup only in truly safe areas.

    About 3-5 feet below the surface, you can find a layer of grainy, faceted snow above or around a crust that formed in mid-January. Sudden and propagating snowpack tests on this layer can indicate the potential for an avalanche. While these avalanches may be less likely below treeline, this weak structure can be found in open terrain above 4,000ft, so we can't rule it out.

    (2/7/2021) A two party involvement occurred on February 7th. Skiers triggered a very large (D3) avalanche which partially buried 2 people. The avalanche released on a NE aspect at 6,100ft on Jim Hill in the Stevens Pass zone.

Avalanche Discussion

The potential for natural avalanches will increase as heavy snow accumulates during the day Monday. Observers on Saturday and Sunday reported several natural and triggered avalanches and widespread shooting cracks. A large natural avalanche in the Old Faithful slidepath even hit Highway 2 near Stevens Pass late in the day Saturday. Avalanches occurred within new and wind drifted snow and at the old/new snow interface. The recent snow rests atop weak old snow surfaces with the potential for surprising avalanches that could be triggered remotely from areas below or adjacent to avalanche terrain. Avalanches related to new snow and wind are concerning enough, and lingering deep slab instability still weighs on our minds. With a busy holiday weekend, be mindful of other backcountry travelers above and below you. These conditions require very cautious terrain and travel choices. Non-avalanche hazards also exist at this time including tree well and deep snow immersion. Find out more information about deep snow safety HERE.

Unfortunately, a snow biker triggered an avalanche on the deep persistent layer in the East Central zone on February 8 and was buried and killed. For more details and information, see the Accident Reports page and the post-incident investigation video below. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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