Avalanche forecast

Stevens Pass

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Large human triggered avalanches are possible, especially on steep slopes near ridgetop. Snow and strong winds have formed thick windslabs near and above treeline. Give these newly created, firm slabs time to heal. Very large deep slab avalanches are unlikely, though still possible on isolated upper elevation terrain.

Avalanche problems

  • Wind Slabs

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

    Although the active wind drifting may have subsided by the time you get out there on Sunday, recently formed slabs will continue to be reactive in the right location with a human trigger. Cohesive slabs rest over the most recent (12/21) melt freeze crust, and any avalanche may propagate wider and run further than expected because of it. Look for indicators such as shooting cracks and strong over weak layering with wind drifted snow. Use test slopes to check how well recent slabs are bonding. Avoid wind exposed slopes steeper than 35 degrees if you find signs of instability or fresh avalanches. Slabs will be deeper and widest in higher elevation, wind exposed terrain, and near ridgelines. You can avoid getting avalanched by seeking out sheltered slopes and terrain less than 35 degrees in angle.  

    Example windslab running on a crust.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    3

    Deep persistent slab avalanches could be very large, big enough to destroy a house. These dangerous avalanches can catch even the most experienced backcountry travelers. Triggering one is unlikely but not impossible. With an added storm load, it is still a good time to tread lightly around areas where you could potentially still trigger one, such as very steep, unsupported, convex and rocky slopes. Any small wind slab could step down, and trigger a monster deep slab. There is lots of uncertainty associated with a deep, weak layer such as this one. Is the 12/21 crust 'capping' instability? In some places it may be, but not all. The best way to stay safe is to avoid where these avalanches may exist. Keep your distance from slopes 35 degrees and steeper that are open enough and tall enough to produce large avalanches. Make sure you're not standing below or adjacent to steeper slopes. Use clues to stay out of avalanche paths, like trees stripped of uphill branches or openings in vegetation that continue up-slope.

    On Thursday, observers in two different locations were surprised to still find test results (CTM (SP), ECTP) indicating that you can trigger these avalanches. You can find a thin weak layer of small facets (and in places surface hoar) above a crust buried about 2-4 feet below the surface. The weak grains have been rounding and gaining strength over the past week. The layer became active on December 14th and was involved in a widespread cycle of large, natural avalanches this past weekend. These avalanches occurred on a variety of aspects above 5,400ft. 

    (12/24/2020) Debris from a natural size D2.5 slab avalanche that likely occurred on the night of Dec 19th. Lichtenberg Mtn, SE, 4,100ft.

Avalanche Discussion

About 7" of new snow has accumulated since Friday, and another few inches may fall by the end of the day Sunday. Southwest winds were strong, and observers reported intense wind transport in exposed locations on Saturday. There is uncertainty about how the new snow is bonding to existing surfaces in upper elevation, alpine terrain.  Previous snow surfaces consisted of this slick crust, surface hoar, near surface facets and wind broken particles. In windward locations, the recent crust could still make for some slick and challenging travel. 

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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