Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

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Limite del bosco
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In sintesi

Another warm and clear day is on tap for the eastern mountains, so look for warming snow and small wet loose slides on solar aspects. At higher elevations, steer around pockets of wind drifted snow that appear rounded or pillow-like. Before jumping into larger alpine slopes, consider the consequence of triggering a larger and more surprising avalanche on a deeper layer. 

Problemi valanghivi

  • Loose Wet

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

    The strong March sun and warming temperatures will make the snow surface wet and weak on solar aspects (E-S-W). You’ll likely see these fan shaped slides on steep sunnies,  especially near rocks and cliffs. Consider steering around these areas if you notice rollerballs and pinwheels. These are often precursors of larger loose wet avalanches. This problem will likely be more prominent at those mid-elevations (and higher) that hold soft snow at the surface.  These should stay small, but still consider the consequence if they push you into a terrain trap such as trees or a gully bottom. 

    (12/3/2022)

    Steer around steep solar slopes if you notice signs like this. 

    Photo: Zack McGill- Cascade Mtn Ascents

  • Wind Slabs

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

    East winds have been at work drifting available soft snow into shallow slabs at mid and upper elevations. Winds have been blowing from several different directions over the last few days, so you may encounter these wind drifted slabs all over the compass. As the day heats up, give cornices a wider margin. Warming temperatures are likely making these things a little weaker and easier to initiate. 

    As you travel, be in tune with changing snow depths and texture. You’ll typically find these slabs lurking on the downwind side of ridges, under cornices, below cliff bands, and near the top of chutes/couloirs.

     Fortunately, this is an easy avalanche problem to navigate around. You can use visual clues to help you identify slopes of concern. Look for active loading or slopes that appear textured and fat. Pillow-like slabs or ripples at the snow surface all indicate wind loaded terrain. As always, pump the brakes if you notice shooting cracks under your skis/sled or hear snow that sounds hollow like a drum. 

    While unlikely, avalanches above treeline could break larger and wider than you may anticipate. Last week's loading event resulted in a couple of very large, natural avalanches above treeline (see photo and discussion below for more details). 

    (3/11/2023)

    Crown of a very large avalanche in the Icicle Creek Drainage. We have a lot of uncertainty surrounding this avalanche problem. But best to make conservative choices in alpine terrain.

    Photo: Matt Primomo

Avalanche Discussion

NWAC forecaster Katie Warren traveled into the Icicle Creek drainage on Thursday. She observed gusty east winds drifting snow near ridgetop, a  generally right-side-up structure,  and found the Valentines crust sitting 3-4 ft below the snow surface. You can check out her full observation here. 

Observations continue to trickle in of isolated, larger deep slabs being reported in heavily loaded, alpine terrain. On Thursday an observer on the east side of Stevens Pass observed a very large avalanche on North Chiwaukum ( 6900 ft, W aspect). This slab appeared to be several days old and likely failed during a significant loading event on the 10th, which was right around the same time that very large avalanches on Cannon Mountain and Rock Mountain were observed. NWAC forecaster Matt Primomo also reported a small, isolated deep slab that likely ran during a similar time period just east of the Swath (NE, 5300 ft). These observations serve as a reminder that triggering a larger slab in isolated, upper elevations areas is not out of the question. 

This low likelihood, high consequence situation is a tricky one. We have a bit of uncertainty regarding the distribution and depths of this weak layer. So, if you plan on traveling in the alpine across the zone, consider these recent occurrences before dropping into larger terrain features at these elevations. 

 

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