Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Sun
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Another round of snowfall with very strong wind will create very dangerous avalanche conditions at upper elevations on Saturday. Large, and often surprising avalanches have been occurring and may be triggered on a variety of weak layers even below treeline. Consider avoiding entire features in avalanche terrain, and stay alert to signs of instability such as shooting cracks and whumphs.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3

    Wide and surprising avalanches are possible if an avalanche runs on faceted grains or buried surface hoar, which could be more than 2.5ft below the surface. This past week, large, human triggered and natural avalanches have likely failed on buried surface hoar. You'll need to carefully evaluate the snowpack to travel safely in avalanche terrain at all elevations. Open slopes from north to southeast aspects and steeper than 30 degrees will be the most likely areas to trigger one of these.

    Surface hoar tends to survive in open, sheltered and shaded terrain. so you could trigger slides even below treeline on convex, and unsupported features. At mid elevations and further east, instabilities within or below a deteriorating rain crust from January could produce persistent slabs with the additional new snow and wind on Saturday. When the snowpack is this complex, keep your terrain choices simple.

    (2/3/2021) A ski triggered avalanche was reported in Portley Bowl on 2/2. The next day an observer took the bottom photograph at 10:50AM. The majority of the rest of the slopes in the bowl had avalanched, with no ski tracks observed in or out of the slides. These may have been solar triggered, and suspected to have failed on a buried surface hoar layer from 1/30.

  • Wind Slabs

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

    Another round of new snow and strong westerly winds will transport the snow as it falls on Friday. Wind slabs could be quite reactive as they rest over a suncrust on solar aspects, and recently buried surface hoar on shaded aspects. Feel for wind stiffened or hollow sounding snow as you enter open areas, and change aspects. Be especially careful of cross loaded gully features and cornices. 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. 

    Example wind slab: Long shooting cracks through wind stiffened snow are direct signs of instability.

Avalanche Discussion

A large ski triggered avalanche was reported from the near treeline band on Friday, and folks reported several small wind slabs in steep terrain below cliff features in Cutthroat drainage. Professionals reported shooting cracks and propagation from steeper terrain as well. On Wednesday, strong sun appeared to have pushed the slopes in Portley Bowl over the edge and caused natural avalanches. This following a ski triggered slab in the bowl on Tuesday. A skier had a close call on Tuesday near an area often thought of as 'safe' ski terrain. We suspect buried surface hoar as the culprit for these past two avalanches.

Outside of wind-affected areas, you may find about 2ft of snow above the Jan 30th interface in the Washington Pass area. Another potential weak layer are small facets within, or above a crust from mid-January. This prominent crust can be found about 3ft below the surface at mid and lower elevations.

Further east in the zone, the weakened crust from mid-January has been a concern, even below treeline. Observers in the Twisp drainage reported collapsing at 4,800ft on a northeast aspect on Monday, and snowpack tests show potential for avalanches to propagate. Also on Monday, a large avalanche was heard in the Lost River drainage following a period of warming and light to moderate precipitation. To sum it up, we have higher uncertainty with the 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. You'll need to evaluate the upper snowpack carefully to travel safely in avalanche terrain no matter where you go on Saturday!

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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