Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

You can trigger large avalanches on weak snow layers buried by the recent snow or on older layers from Mid-November. The variable distribution of these conditions throughout this large zone will make it important to approach new terrain cautiously. Use small, inconsequential test slopes to see how the snow reacts. If you see shooting cracks, feel the snowpack collapse, or the test slope produces a mini avalanche, you should stick to lower angle terrain. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    During the storm from 12/8-12/9, avalanches ran on the mid-November facets at Mission Ridge, Crystal Mountain. We suspect that a couple of observed avalanches in the East North zone also involved older weak snow layers. These avalanches ran naturally, during control work, and by skiers in backcountry terrain. Avalanches involving weak persistent snow layers are tricky and tend to stick around for a while. The snowpack will seem to adjust over time to a new snow load, then another storm rolls into the mountains, and we see avalanches breaking down onto these older layers again. Someone hitting a shallow spot near rocks or cliffs also can trigger these avalanches or large triggers such as explosives during avalanche control work. This uncertainty should make you take a step back and closely evaluate slopes that may harbor this weak snow. Steep, northerly aspects are the most suspect location for these deeply buried weak layers to exist. Be particularly suspect of steep open terrain below ridges, areas with stiff wind drifted snow, steep rolls in the middle of slopes, and near rocks or cliffs where you are more likely to trigger these avalanches. Dig down and identify sugary, faceted layers or feathery surface hoar layers buried in the snowpack. You can also use small test slopes to see if you can get a slab of snow to move. Stay on lower angle slopes if you find the overlaying snow slides easily on these layers, experience whumping collapses, or observe cracks shooting out from your equipment.

    (12/10/2022)

    3ft deep persistent slab avalanche in a heavily wind loaded area at Mission Ridge

    Photo: Drew Carlton

Avalanche Discussion

Many locations in the East Central zone have a weak snowpack structure, with the weekend's storm snow overlaying recently buried surface hoar/facets and a deeper layer of weak, sugary facets from mid-November. Most evidence of avalanches on these deeply buried facets are from northern aspects in wind-loaded terrain near and around Blewett Pass and Mission Ridge. Add into the snowpack mix the recently buried surface hoar from 12/8, and we have a complicated snowpack throughout the East Central Zone. In addition, we have significant uncertainty about the distribution and reactivity of these weak layers. While reports from the Teanaway and Salmon La Sac areas may indicate a decreased likelihood of triggering these avalanches, we are still gaining confidence in the spatial distribution of avalanches on this layer. An NWAC forecaster in the Icicle Creek area noted some cracking on the 12/8 new/old snow interface and found small buried near surface facets to be the culprit. This 12/8 interface is also where you can find buried surface hoar in some locations. Whichever weak snow grain you may find, it will take longer than usual for this storm snow interface to strengthen. Uncertainty surrounding the reactivity of these layers is high, and you should assess the snowpack before committing to steep terrain. 

The sun has been warming southern aspects, and now most sun exposed terrain has a melt freeze crust on the surface. Some small loose avalanches were observed near the Icicle Creek area on Tuesday and nother sunny day is in the forecast for Wednesday, with slightly warmer temperatures. Snow on steep, southern aspects may get heavy and wet. You could see roller balls or wet snow sliding off steep terrain near rocks or cliffs. Stay out from under cliffs or rock faces that begin to shed snow. 

If you are out and about in the mountains, you can help us by submitting an observation. 

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