Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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In sintesi

Winds will increase overnight on Wednesday, drifting the recent snow into stiff slabs where you could trigger an avalanche. While these avalanches will likely be small, they could be easy to trigger and have high consequences in extreme terrain. Stick to lower-angle slopes if you observe shooting cracks or whumphing collapses. 

Problemi valanghivi

  • Wind Slabs

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    Increasing winds will drift the recent snow into more cohesive wind slabs on lee aspects. They may be quite reactive where they formed over weak snow surfaces. Wind slabs will likely be shallow and isolated to mid and upper elevations with a more consistent snowpack. While they won't be a significant hazard for most backcountry travelers, use caution in extreme terrain where a slip and fall could have high consequences. Likely spots to find these small wind slabs are below sharp ridgelines, at the top of confined gullies, or the base of cliffs. Textured surfaces, deeper drifts, and cornice formations can also help you identify likely wind slab locations. 

    Recent snow totals vary throughout the zone, and new snow fell on various weak and slick surfaces, including surface hoar, faceted snow, and melt-freeze crusts. As you travel through the terrain, monitor the new snow depths and how the new snow bonds with the underlying surface using quick hand pits or test slopes. If you find more than 6-8 inches of snow that slides easily on older layers, choose more conservative terrain to prevent getting surprised by a small avalanche.

    (4/8/2023)

    You may be able to trigger shallow wind slabs like this on Thursday. 

    Photo: Mission Ridge Ski Patrol

Avalanche Discussion

A storm favoring the east slopes of the Cascades brought 4-6 inches of snow to East Central along with calm winds. The new snow buried weak old surfaces, consisting of surface hoar and facets over a thin crust. Below this fragile crust is another layer of weak snow over a more robust series of crusts. On Wednesday, NWAC forecasters in multiple zones, including East Central, found that this new interface (1/2 SH) was reactive in snowpack tests. With very light winds and just a few inches of low-density snow, there wasn't much of a cohesive slab over this layer at the time. But as the week progresses, we will be in a "trickle-in" weather pattern with light snow and increasing winds, slowly building more of a slab on top of these suspect weak layers. So expect a slow and steady increase in the avalanche danger moving forward as well. As we approach the weekend, a more robust storm system may be quicker to overload these layers. 

We have been tracking more deeply buried weak layers that have produced unstable snowtest results in some locations. So, as we gradually build a more robust slab over these weaknesses, approach new terrain slowly and carefully monitor how well the new snow bonds with the old surface. Quick hand pits, test slopes, and shovel tilt tests are great ways to identify weak layers with soft storm snow. Be particularly suspect of lee slopes below ridges, the base of cliffs, and confined alpine features where winds drift snow deeper and stiff slabs may form faster than in sheltered terrain. 

The snow cover is still shallow. You may encounter exposed creeks, rocks, and logs at lower and middle elevations. 

If you get out, let us know what you see by submitting a public observation!

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