Lawinenlagebericht

Stevens Pass

Northwest Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
4 · Gross
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
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Kernpunkte

This weekend is a good time to stay off of, and out from underneath steep open slopes due to very dangerous conditions. Weak snow over a crust has been the culprit for wide and surprising avalanches over the past few days, and this trend is expected to continue. At upper elevations, you may trigger an avalanche from a distance. Below treeline, travel cautiously, carefully assess recent layers of the snowpack and consider what is above you. Conditions will become more dangerous Saturday evening into Sunday as a major storm makes landfall.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    2–3

    There are two persistent weak layers between 1.5 and 2.5ft deep in the snowpack throughout the zone. The slab on top has been gradually getting thicker over the past few days, and seasoned backcountry travelers have been surprised when they triggered very wide avalanches from a distance. Another storm with strong wind overnight Friday will add to the stress on these layers, and cohesive wind slabs will form in exposed locations. By Saturday these avalanches will be nothing to mess around with.  If you do travel to mid and upper elevations, stay well away from any steep open slope. If you initiate a shallow wind slab on the surface, it could step down to the crust and become a very large and destructive avalanche. Keep it conservative and don't roll the dice with steep slopes near and above treeline.

    A few of the recent slides that we have information on: 

    12/17-Northeast aspect at 5,800ft above Lanham Lakes: 15-20" deep, 500'wide. Remotely triggered by a party of two.

    12/17- Southwest aspect at ~5,500ft above Valhalla Lake: D2 avalanche with debris down near the lake. Natural avalanche.

    12/16-Northeast aspect at 5,400ft: 16" deep, 110' wide. Remotely triggered by party of two.

    (12/18/2020) Part of a persistent slab avalanche (D2) that was ~500ft wide and 15"-20" deep. The avalanche was unintentionally and remotely triggered by experienced backcountry skiers on 12/17. The avalanche ran on weak snow over the 12/9 crust.

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    Another storm will lay down a new layer of snow on the pass. Temperatures are forecast to warm up as it comes in, making for an upside-down feeling snow surface. Steer around any open slopes greater than 35 degrees, and if you find signs of instability such as cracking and small avalanches on steep slopes. Use small slopes and hand pits to see which storm layers may fail. Above 5,000ft, there is potential for any shallow avalanche in the surface layers to step down to the crust and become a much larger slide. 

    Storm slab instability on a small convexity below treeline.

Avalanche Discussion

By Saturday morning, roughly 1.5 to 2.5ft of snow are likely to be resting over the prominent 12/09 melt freeze crust. A layer of buried surface hoar can be found in many areas 3-6" above this crust, and storm layers from the week have shown ability to fracture and create avalanches on their own. Above 5,000ft folks have remotely triggered wide avalanches in some drainages, but not in others. The upper elevation snowpack is tricky. There is enough uncertainty that it is a full gamble to get on any steep slope above 5,000ft at the moment. As the storm pattern continues, so does the size of the avalanches we are seeing. 

At lower elevations (well below treeline), the snowpack has been more stable. Instead, anticipate evaluating the new snow and how it bonds to the layer beneath it. Areas of thin coverage, open creeks, and shallowly buried obstacles still require your attention to navigate safely. 

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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