Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Strong wind and some new snow will create dangerous conditions at upper elevations on Thursday.  Large and surprising human triggered avalanches have likely run on a layer of buried surface hoar in the zone.  Consider avoiding slopes steep enough to avalanche at all elevations where wind has created cohesive slabs, and stay alert to changing conditions throughout the day.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

     Wide and surprising avalanches are possible if an avalanche runs on buried surface hoar, which could be up to 2ft below the surface. Strong westerly winds will continue to transport new and recent snowfall onto lee slopes on Thursday. With recent, large human triggered avalanches likely failing on buried surface hoar, you'll need to carefully evaluate the snowpack to travel safely in avalanche terrain. Wind loaded slopes from north to southeast aspects, and steeper than 33 degrees will be the most likely areas to trigger one of these. Feel for wind stiffened or hollow sounding snow as you climb in elevation and change aspects. Be especially careful around places like convex rollovers and unsupported slopes. Watch for shooting cracks or whumphing collapses as a clear sign of instability.  Wind slabs could also step down to other weak snow layers in the top 2ft of the snowpack.

    Outside of wind affected areas, loose dry avalanches may run and entrain new snow on steep slopes. Don't let a small loose avalanche ruin your day by pushing you into terrain traps or strainers. 

    (2/2/2021) Ski triggered avalanche in Portley Bowl. East aspect at ~7,000ft. Photo by James Schick.

Avalanche Discussion

Two large, ski triggered avalanches were reported late in the day on Tuesday. With recent observations of buried surface hoar from January 30th, we have to suspect this layer as the culprit (Guilty, until proven innocent)! Observers reported about 1.5' of snow above the Jan 30th interface in the Washington Pass area. This layer presents as surface hoar or a thin sun crust on solar aspects. Professionals found this layer as small surface hoar at 5,700ft in Cutthroat on a southeast aspect, with clean planer results with tilt tests. Another potential failure layer is small facets over a crust, which can be found about 2ft below the surface. 

Further east in the zone, observers in the Twisp drainage experienced collapses at 4800' on Monday. Snowpack tests showed the potential for propagation 1.5 feet down on the Jan 24th weak snow (facets) layer on shaded aspects at 5700'.  Also on Monday, a large avalanche was heard in the Lost River drainage following a period of warming and light to moderate precipitation. This ties into an observation in the eastern mountains from last Wednesday reporting cracking and collapsing on older facets in snow from early January.  To sum it up, we have higher uncertainty with a shallower and weaker snowpack in the eastern part of the zone. If you travel to areas such as the Chelan-Sawtooth Mountains, Twisp River, and Chewuch drainages, take time to dig in the snow and look for older weak layers. Consider traveling in lower angle terrain and smaller terrain features.  You'll need to evaluate the upper snowpack carefully to travel safely in avalanche terrain.

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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