Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

An easterly flow event brought just enough snow to refresh surfaces and build shallow, wind-drifted slabs at upper elevations where you could trigger an avalanche. While these avalanches would 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

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1

    Thin wind slabs at upper elevations may be quite reactive where they formed over weak snow surfaces. They are likely only 4-6 inches deep and in isolated pockets of terrain at the highest elevations. So, while they won't be a significant problem for most backcountry travelers, use caution in extreme terrain where a slip and fall could have high consequences. Likely spots to find these dinner table-sized wind slabs are below sharp ridgelines, at the top of confined gullies, or at the base of cliffs. Textured surfaces, deeper drifts, and cornice formations can also help you identify likely wind slab locations. This new snow fell on various weak and slick surfaces, including large surface hoar, faceted snow, and melt freeze crusts. As you travel through the terrain, monitor how the new snow bonds with the underlying surface using quick hand pits or test slopes. If the snow seems to slide easily, more conservative terrain selection is warranted to prevent getting surprised by a small avalanche. 

    (12/31/2023)

    You may be able to trigger small wind slabs in alpine terrain, like in this example. 

     

Avalanche Discussion

An easterly flow event is bringing 3-5 inches of snow to the east slopes of the Cascades. It's not much, but it is a welcome change. The upper snowpack has multiple weak layers, and the few inches of new snow buried weak snow surfaces. As we build a cohesive slab over these layers, we'll monitor to see if they will persist and become a longer-lived avalanche problem. 

An observer triggered a small pocket of wind slab on a lee aspect on 12/31, and Mission Ridge Ski Patrol triggered small wind slabs with explosives on 12/30. These avalanches occurred at upper elevations in wind-loaded northerly terrain and were 8-16" deep, failing on a weak layer above the mid-December melt-freeze crust. With the fresh snow and wind, we may see a few more of these types of avalanches. So, ease into alpine terrain slowly and keep your terrain selection conservative if you see cracks shooting away from you or hear loud audible collapses. 

NWAC forecasters and observers have found a weak upper snowpack structure near Blewett Pass, Mission Ridge, Dirtyface Mountain, and Holden. The 12/19 crust/facet layer and some buried surface hoar layers have produced unstable snowpack test results. While we are tracking the development of this weak structure, there is no significant avalanche hazard until we receive some additional snow.

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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