Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

It remains possible for you to trigger avalanches in pockets of wind drifted snow on Thursday. Steer around slopes that appear wind textured and rounded. As the day heats up, consider moving off of steep solar aspects especially if you notice rollerballs or pinwheels.

Problemi valanghivi

  • Wind Slabs

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

    The past two days have offered all the ingredients( new snow, strong winds, and long duration of wind speeds) needed for some hard, stubborn wind slabs to form. And now to mix things up - winds are shifting more easterly - so you may notice these wind drifted slabs forming in less common areas like west aspects. 

    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 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

  • Loose Wet

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

    Pretty straightforward here… the sun will make an appearance and make the snow surface wet and weak on solar slopes. You’ll likely see these fan shaped slides on steep solar slopes, especially near rocks and cliffs. Consider steering around these areas if you notice rollerballs and pinwheels. These are often indicators telling you that the snow surface is getting weak and that larger loose wet avalanches may soon follow. This problem will likely be more prominent at those mid-elevations (and higher) that hold soft snow at the surface.  These should be small, but still consider the consequence if they push you into a terrain trap such as trees or a gully bottom. 

    Consider moving to shadier slopes if you notice signs like this.

    Photo: Joe Dellaporta

Avalanche Discussion

On Wednesday, NWAC Forecaster Matt Primomo reported a small, isolated deep slab that likely ran a few days ago just east of the Swath (NE, 5300 ft). This slab was small, but serves as a reminder that triggering a larger slab in isolated pockets at upper elevations is not out of the question.  Avalanche professionals at Holden Mine reported natural avalanches during the storm on Monday (including seeing powder clouds from avalanches) along with a few small loose wet avalanches on Tuesday. Storm totals on Monday showed a large spread with the most snow falling in the northwest portion of the zone near Trinity and Holden (nearly 1ft with 0.9" of water). Weather stations in the Salmon la Sac area picked 6-8" and the Wenatchee Mountains received 2". The stormy weather and poor visibility prevented extensive observations. A very large, natural avalanche ran in Tumwater Canyon between Cabin ck and Fall ck (see photo above).

The recent snow has piled deep over a couple of intermittent sun crusts and a pair of rain crusts from Valentine's Day, which can be found 3-5ft deep. Very large avalanches that occurred on the 10th on Cannon Mountain and Rock Mountain may have run on these crusts (or some other deep layer).  The Valentine's crust often presents as a crust/facet/crust sandwich, with weaker snow beneath the upper crust. Observations indicate wide variability in the structure and depth of this layer throughout the zone.

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