Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Another round of alpine winds and light snow on Thursday means wind slab avalanches are likely below ridgelines and steep slopes with freshly drifted snow.  Watch for loose avalanches on very steep slopes at lower elevations and in wind-sheltered terrain.  Take the time to evaluate the snowpack if you're headed to further-flung areas of the zone,  avalanches may become large if they step down to weaker older snow layers. 

Problemi valanghivi

  • Wind Slabs

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

    Winds will continue to drift new and recent snow near and above treeline Thursday.  You could trigger wind slab avalanches on the leeward sides of ridges and on cross-loaded terrain features at upper elevations.  Take note of which aspects have new or recently drifted snow as you change aspect and elevation. 

    Blowing snow, stiff, firm snow surfaces, and cracks shooting through the snow are all signs that you could trigger a slide. You can avoid these avalanches by sticking to sheltered terrain, traveling on slopes under 35 degrees, or choosing slopes where the wind isn't drifting snow. 

    (2/11/2021) An example of cracks shooting through the snow in wind-exposed terrain near Stevens Pass. This is a warning sign that you could trigger a wind slab avalanche. Photo: Josh Hirshberg

  • Loose Dry

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

    You can trigger dry loose avalanches on slopes 40 degrees and steeper where you find light, soft snow on the surface.  Don't let a small loose avalanche catch you off guard and push you over cliff bands,  into trees or bury you in a gully.  

    (2/9/2021) Dry Loose avalanches start at a point and fan out as they run downhill. Don't get knocked off your feet or pushed into a terrain trap. Photo: Zack Wentz

Avalanche Discussion

About 8-10 inches of snow has accumulated over the last 48 hours in the Hwy 20 corridor.  Ridgeline winds have continuously moved snow onto lee slopes over this period with several small natural and human-triggered soft slab avalanches reported in wind stiffened snow Monday night and Tuesday.   An incoming frontal system on Thursday will produce a few inches of new snow by the end of the day and bring increasing ridgeline winds.  

While persistent slab avalanches are unlikely, they're still on our minds in outlying parts of the zone west of Washington Pass and in the eastern mountains. On Wednesday 2/17, an observation from the Twisp River drainage in the near treeline band found the mid-January facet/crust combo unreactive in snowpack tests and over 3 ft down.  Buried surface hoar slightly closer to the surface,  less than 3' or 80 cm down, showed sudden results in snowpack tests. No new or recent avalanches down to this layer or other signs of instability like whumpfing, or collapsing were noted.  Further west, the last persistent slab avalanche occurred near Rainy Pass on Feb 8th (see photo below). It is suspected to have run on the mid-January crust-facet layer about 2-3ft below the snow surface. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources. Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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