Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

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

Look for and avoid steep terrain features holding recently wind drifted snow. You are most likely to trigger an avalanche on slopes where you observe the wind depositing snow on downwind slopes. The Mountain Loop and areas near the Passes and the Cascade Crest are forecast to see slightly higher wind speeds  - and more wind slab formation - on Thursday.

Avalanche problems

  • Wind Slabs

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

    Slab avalanches in new snow and wind slab layers were reported from the Mountain Loop. These will gain strength and become more difficult to trigger Thursday but they still pose some hazard, especially in consequential terrain. 

    If you trigger a slab avalanche Monday it would likely be on a steep downwind slope just below ridgeline or on terrain features like convex rollovers, gully walls, or around cliffs and rock outcroppings. Look for blowing snow, changes in snow consistency, or visual clues like cornices and wind-scoured ridgelines to identify areas of wind slab

    Test slopes and hand pits can help you monitor differences in layering as you change aspects and gain elevation. Evaluate the bond of wind slabs and ease into steeper terrain - or just find a lower-angled line around areas like convex rolls where you are more likely to trigger one.

    (4/12/2023)

    Small human triggered slab avalanche in wind loaded terrain on Shuksan Arm. North aspect at 5400'.

    Photo: Adam Ü

Avalanche Discussion

The amount of wet loose avalanche activity Wednesday varied across the west slopes. Some zones saw a rapid cloud build-up that limited warming. Other areas like the Baker Backcountry and Snoqualmie Pass saw more consistent sun and then wet loose avalanches on southerly aspects. More clouds are forecast for Thursday but you could still see wet avalanches, especially in the morning. Keep track of what’s going on above you and be ready to adjust your plan anytime it starts to warm up.

Wednesday brought sun, powder snow, and good visibility to observe both recent avalanches and also those from the storm and rain event on Sunday. A team in the northern Mountain Loop found easy to trigger slab avalanches on multiple aspects at upper elevations. They were small in size but still appeared to pack enough of a punch to take a person for a ride. While none were reported to be big enough to bury a person, small avalanches like these can have high consequences with cliffs, rocks trees or gully features in the runout.

Numerous natural and also a few human triggered slab avalanches - most D1.5 or less -  were found around West North. A handful of very large avalanches (D2.5-3) were also reported from West Central (photo 3) ad West North (photo 6). Most of these are suspected of releasing during the last big storm and rain event.

Solar aspects should have some sort of crust for the rest of the week while shaded aspects hold excellent snow. Below the most recent snow, the upper snowpack structure is comprised of dense rounded grains separated by melt-freeze crusts formed by rain and sun. While it is unlikely a person could trigger a slab avalanche below the old-new snow interface, larger avalanches out there show us that deeper layers can always wake up with heavy loads of new snow, rain, or big triggers like cornice fall or a smaller avalanche.

 

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