Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

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

Strong west winds with up to 1 foot of snow will again form dangerous avalanche conditions. Avoid large slopes 35 degrees and steeper, especially where recent westerly wind forms thick slabs. You may still be able to trigger unsurvivable deep slab avalanches.

Problemi valanghivi

  • Wind Slabs

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

    You can trigger avalanches on wind-loaded, leeward slopes 35 degrees and steeper. Steer around thickly loaded and pillowed features. Avoid convex rollovers and slopes steeper than 35 degrees. Fresh wind slabs will form throughout the day. They'll grow bigger and become easy to trigger as the day goes on. You can expect more dangerous conditions near and above treeline. Due to both fresh wind slabs and the potential for deep slab avalanches, you should avoid large avalanche paths, especially at mid and upper elevations. Below treeline, stick to wind-sheltered slopes and well-supported features. Even in sheltered terrain you can trigger small storm slabs and loose avalanches on shaded slopes steeper than 35 degrees. 

    (1/28/2021) An example of wind slab on Tye Peak. Photo: Marc Simonpietri

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    3–4

    The best way to stay safe is to avoid large avalanche paths and overhead start zones. Avoid traveling below large slopes 35 degrees and steeper. Slopes 5,000ft and higher and on sun-exposed aspects are of most concern. 

    With another rapid load of snow expected through Friday, it's too soon to take Deep Persistent Slab avalanches off our minds. On Sunday and Monday, widespread natural avalanches ran big enough to destroy cars and houses. Some of these ran 2-3,000ft to the valley floor and involved a weak layer of facets and a crust that was buried in mid-January. While Solar aspects appear to have been especially problematic, we know deep slabs have also run on shaded north and northwest aspects.

    (2/24/2021) At the top of the ridge, you can see the crown of a very large avalanche (D3.5) in the Wellington slide path, just west of Stevens Pass. This avalanche ran on Feb 21st and may have involved a weak layer buried in mid-January. Windy Mtn, SE, 5,400ft. Photo: Josh Hirshberg

Avalanche Discussion

Expect up to 1 foot of new snow by Thursday evening with strong westerly winds. This will fall on a sun crust that formed on steeper sunny slopes on Wednesday. On the 22nd, rain fell on previously dry snow to about 4,800ft. The crust is now buried as deep as 3 feet. From the 20-23rd, the Schmidt Haus weather station has registered about 6" of water equivalent. Numerous very large natural avalanches ran during that time:

Tuesday- Stevens Pass Patrol triggered numerous storm slab avalanches size D1.5-2. They triggered one larger size D2.5 in the recent storm snow. on a solar aspect. 

Monday- Observers reported D3 sized natural avalanches on a ESE aspect at 5,200ft near Skyline Lake (in the Moonlight area). These were at least 7ft deep, knocked down trees, and may have run on the 22nd. A similar avalanche was reported on a SW aspect, near 5,100ft on Nason Ridge, just west of Rock Mtn. In the Scenic area, guides reported size D3 natural avalanches running on the mid-January weak layer 3-10ft deep on W-N aspects. Natural avalanches ran on SE and SW aspects of the Tunnel Creek area to D2.5. WSDOT triggered a very large size D3 in one of the Old Faithful paths on a SW aspect below treeline. Observers reported natural avalanches to size D3 on a SE aspect of Lichtenberg Mtn as well as a D4 sized avalanche on a SE aspect of Rock Mountain in Schilling's creek. This avalanche broke many mature trees and deposited debris 40 feet high near Highway 2. 

Sunday- Observers reported a very large D3.5 natural avalanche in the historic Wellington slide path on a SE aspect of Windy Moutain.

Saturday- A very large avalanche (likely skier triggered) ran on the mid-January weak layer, 5 feet below the surface, on a S aspect at 5,000ft, below Skyline Lake.

 

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