Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

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

Dangerous avalanche conditions remain on the heels of a major storm and avalanche cycle. Avoid large slopes 35 degrees and steeper, especially where recent westerly winds formed thick slabs. You may still be able to trigger unsurvivable deep slab avalanches.

Problemi valanghivi

  • Storm Slabs

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

    You can trigger avalanches on slopes steeper than 35 degrees. Due to deep slab avalanches, you should avoid large avalanche paths, especially at mid and upper elevations. Below treeline, stick to lower-angle slopes and small, well-supported features. Storm slabs and loose wet avalanches could become easier to trigger on sun-exposed slopes. Recent strong westerly winds built thicker slabs on leeward slopes near and above treeline and stressed old weak layers (see below). Wind slabs alone could be very large and destructive and they could result in unsurvivable, deep slab avalanches. 

    (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

    These avalanches are unsurvivable and it's not possible to manage them. 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. Most of these avalanches originated from slopes 5,000ft and higher.

    Wednesday will be the first time we'll have seen ridge tops since at least the 16th, if not longer. Even professional experts are unsure of the current likelihood of Deep Persistent Slab avalanches. We do know that many natural avalanches ran on Sunday and Monday 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 deeps slabs have also run on north and northwest aspects. With the storm just barely behind us, the threat of these very dangerous avalanches remains.

     

    (2/23/2021) A destructive natural avalanche ran to Highway 2 in the Gaynor path on Feb 22nd. It deposited a very large pile of debris and broke several trees. Rock Mountain, SE. Photo: Josh Hirshberg

Avalanche Discussion

On Monday, rain fell on previously dry snow to about 4,800ft and was further buried as temperatures dropped. The crust is now buried as deep as 3 feet. As of 5p on Tuesday, the Schmidt Haus weather station has registered close to 6" of water equivalent since the 20th and about 10" of water in 11 days. Numerous very large natural avalanches ran over the past few days:

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. Observers reported D3 sized natural avalanches on a ESE aspect at 5,200ft near Skyline Lake (in the Moonlight area). These were 4-5ft 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. 

Monday- 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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