Avalanche forecast

East Slopes North

Northwest Avalanche Center
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Avalanche danger

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

Large and surprising natural and human triggered avalanches have occurred in the zone, running on a variety of weak layers. New snow and strong wind will continue dangerous conditions at upper elevations on Friday.  Consider dialing back your terrain significantly, avoiding entire features where wind has created cohesive slabs, and stay alert to signs of instability such as shooting cracks and whumphs.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2

    Wide and surprising avalanches are possible if an avalanche runs on buried surface hoar or a crust which could be more than 2ft below the surface. 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. 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 be cognizant in unsuspecting rollovers and unsupported features even below treeline. 

    Observers have noted instabilities below treeline within or below a deteriorating rain crust from January. 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

    New snow and strong westerly winds will continue to transport snow onto lee slopes 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 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. 

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

Avalanche Discussion

Two large, ski triggered avalanches were reported late in the day on Tuesday, one of which was a close call, and on Wednesday suspected natural avalanches were observed in Portley Bowl. With recent observations of buried surface hoar from January 30th, we suspect this layer as the culprit. 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 within, or above a crust from January 13th. This prominent crust can be found about 2ft below the surface. 

Further east in the zone, the weakened crust from January 13th 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. 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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