Lawinenlagebericht

East Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

At higher elevations, triggering avalanches in wind-drifted snow is the main concern. Avoid steep terrain where you find deep drifts of stiff snow. In areas near Blewett Pass and Mission Ridge, keep your distance from large terrain features and areas where avalanches could start as there's still a chance of triggering slides on older buried weak layers. 

Lawinenprobleme

  • Wind Slabs

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

    You may be able to trigger these avalanches near ridges, the base of cliffs/rocks, or convex rolls in terrain. You can recognize wind slabs by their pillow-like form and potentially hollow sound. Use cornice formations and drifts behind trees or rocks to identify likely wind slab locations. You can also use your probe or pole to feel for stiffer layers over softer layers. Steer around these wind slabs in steep terrain. Cracks shooting through the snow is a sign to dial back your slope angles. 

    We have significant uncertainty and limited information on snowpack conditions from alpine terrain. 4-6 inches of snow accumulated at the upper elevations in the last two days along with moderate ridgeline winds. This pattern built shallow, sensitive wind slabs on lee aspects. Avalanches may be easy to trigger where they rest on slick melt-freeze crusts. 

    (1/3/2023)

    These pillow-like drifts in the foreground and the cornices in the background are signs that wind slabs exist on the slope below. 

    Photo: Katie Warren

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    1.5–2.5

    Avoid slopes over 35 degrees and large pieces of terrain where you find a layer of buried surface hoar. Persistent weak layers can break widely across terrain features and result in dangerous avalanches. You may be able to trigger the layer if your snow machine digs below the surface or even on foot from thin spots near rocks. The most suspect terrain is above 5,500ft and is relatively sheltered, with sparse tree cover. Meadows and glades are prime locations for preserved surface hoar lurking in the snowpack. 

     We have uncertainty around its distribution. The layer of feathery grains, buried on January 4th, has been reported as widespread near Mission Ridge. If you're traveling in the Wenatchee Mountains, dig down and look for a stripe of feathery grains buried 1-2 feet below. Before this storm, numerous persistent slab avalanches failed on buried surface hoar near Mission Ridge and Blewett Pass. While rain has destroyed this layer at most elevations up to around 5500ft, it is still preserved at upper elevations, though even there it may be capped by a supportive crust.  and scoured ridgelines.

    (1/7/2023)

    An example of what buried surface hoar looks like within the snowpack.

    Photo:

Avalanche Discussion

On Monday, an observer reported shooting cracks and breaking out a small wind slab near Mission Ridge at 6,700ft, NE. You will find challenging travel conditions at low and mid elevations with unconsolidated wet snow and slick crusts. Other hazards should also be on your mind as creeks have opened up and other obstacles are poking their way back out of the snowpack.

Before the last storm, some suspect avalanches occurred at higher elevations in the Icicle Creek area, along with observations of weak faceted grains and unstable snowpack test results. At the same time, observers in other locations found a relatively stable snowpack. This is due to a multitude of previous snow surfaces that varied substantially throughout the terrain. We have minimal information from above 5000ft since this storm. There are observations of preserved buried surface hoar in the Mission Ridge area above 5500ft, but we don't have much information from other locations in the zone. A previously spatially variable snowpack and few recent observations give us significant uncertainty in slope stability in alpine terrain. Anytime there is increased uncertainty, larger margins of safety are necessary to account for unknown conditions. So if you are venturing out into higher elevations, approach new terrain slowly and assess the snowpack as you travel. As you travel, wind slabs, weak snow layers, and icy surfaces should all be on your radar. Look for signs of instability, such as recent avalanches, actively blowing snow, shooting cracks, and collapsing. This is bullseye information on unstable snow, meaning you should dial back your terrain to low-angle slopes. 

Thursday's storm resulted in a widespread natural cycle with wet avalanches up to D3 and many smaller storm/wind slabs. Friday morning, the WSDOT NCR avalanche crew reported multiple D2 wet slab avalanches, with a couple up to size D3. The snowpack is draining water, temperatures are cooling, and the main event seems to be behind us. We are just beginning to get a handle on the extent of this avalanche cycle and the current state of the snowpack. 

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