Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

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

An incoming front will bring increasing winds to exposed ridgelines and alpine terrain as the day progresses. Look for small, freshly forming slabs as you gain elevation. Consider your terrain choice in regard to lingering potential to trigger large avalanches on old layers of weak, faceted snow. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Westerly winds will pick up as the day progresses, and begin drifting snow in the alpine. The snow has been sitting around for a while now, and surfaces are a mixed bag of crusts and facets. Not all surfaces are conducive to drifting into slabs. Lots of weak, faceted snow does exist though, so there is still plenty of snow available to be drifted by the wind. Look for snow grains bouncing over ridgelines, and plumes on the higher peaks. 

    Feel for stiffer snow and look for cracking within any fresh drifts that you find. Steer around steep slopes that are freshly loading. 

    (12/14/2022)

    Example photo showing blowing snow from alpine ridgelines.

    Photo: Willie Webster

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Avalanches involving persistent weak layers are difficult to predict and tend to stick around for a while. Even well after a storm, it may only take choosing the wrong piece of terrain to trigger an avalanche. Pick your routes carefully and defensively if you choose to enter avalanche terrain. Dig down and identify sugary, faceted layers or feathery surface hoar layers buried in the snowpack. You can also use snowpack tests to look for sudden or propagating results. Stay on lower-angle slopes if you experience whumping collapses or cracks shooting through the snow.

    The most likely location for triggering an avalanche is on higher elevation north and east facing slopes where the wind is freshly drifting snow onto slopes. Be 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. 

    (12/10/2022)

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

    Photo: Drew Carlton

Avalanche Discussion

Expect a transitional day on Saturday with some high clouds, some sun, and increasing wind.

The last storm ended last Sunday and the snowpack has settled down significantly. Travel conditions have generally become easier and are not as bottomless as they once were. There are still 'pockets' where you might be able to trigger avalanches due to the lingering weak layers described above. An observer noted a collapse west of Mission Ridge on Thursday, along with three slab avalanches, two of which were in unusual locations. Although isolated, it signals that the snowpack is not fully healed yet. Surface conditions are best described as a 'mixed bag'. My observation from Dirty Face Mountain on Thursday may describe it well. Expect fast, soft recycled powder with some surface hoar on shaded slopes, and various thicknesses of crusts on southeast through southwest aspects. Pay attention to what is on the surface, because it is about to get covered up with light snowfall...what you find on the surface may become another weak layer as the active weather continues into the week.

Many locations in the East Central zone have a weak snowpack structure with facets formed in mid-November buried near the ground. Most avalanches on these deeply buried facets were on 12/8 and 12/9, and observed from north and east aspects in wind-loaded terrain near Mission Ridge. Observations indicate that the snowpack is deeper and the weak layers are stronger in the Teanaway drainage and the Salmon La Sac areas.

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

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