Avalanche forecast

Stevens Pass

Northwest Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Expect dangerous conditions with actively forming wind slabs over weak surfaces. Stay off of slopes steeper than 35 degrees if you find more than 8" of new snow and signs of instability such as shooting cracks. Wind slabs will be thickest at upper elevations near ridgetops. Very large deep slab avalanches are still possible on isolated upper elevation terrain.

Avalanche problems

  • Wind Slabs

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

    Some 8-12" of new snow is expected with the storm into Saturday afternoon. Strong winds with cool temps will create reactive windslabs over the most recent (12/21) melt freeze crust. This new snow is stacking up over a variety of weak surfaces including the slick crust, surface hoar, near surface facets and wind broken particles. Freshly formed wind slabs could be surprisingly reactive, and may only need a persons weight to trigger one. Look for blowing snow, and instability such as shooting cracks. Use test slopes to check how well the new snow is bonding. Avoid steep open slopes 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 dangerous slopes by seeking out sheltered slopes and terrain less than 35 degrees in angle.  

    (12/24/2020) Cracks in recently drifted snow. On Thursday, drifts and pockets of wind slab were easy to trigger. Lichtenberg Mtn, SE, 5,000ft

  • 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, this is the 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

Expect light to moderate snow showers on Saturday, with strong southwest winds.  The winds combined with new snow and cool temps could make for a blustery day. Underneath the new snow, the recent crust could still make for some slick and challenging travel.  There is uncertainty about how the new snow will bond to existing surfaces.

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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