Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You could still trigger shallow wind slabs in upper elevation and exposed terrain. Look to avoid areas with wind textured or drifted snow on steep and unsupported slopes. Deep persistent slabs are unlikely, but continue to consider their consequences as you move about in the mountains.

Problemi valanghivi

  • Wind Slabs

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

    Shallow wind slabs released naturally from alpine terrain on Sunday, and wind continued to drift snow into the day on Monday. Steer around obvious wind features like textured or drifted snow, and wind pillows. Shooting cracks or hollow-sounding snow are signs you could trigger an avalanche on similar slopes.Identify terrain such as steep and unsupported areas of slopes to avoid. 

    If there are sun breaks during the day, keep an eye out for moist, sticky snow and rollerballs. These are all good indicators that wet loose slides could happen on steep slopes of similar aspects.

    (3/8/2021) Wind textured snow with a recent, shallow wind slab in alpine terrain of White Pine Cirque.

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    3

    Deep persistent slab avalanches are unlikely, but not impossible. For this reason, maintain a conservative mindset as you travel in the backcountry. Know that these deep persistent slab avalanches could still happen, because the snowpack structure needed still exists. The last recorded one was on March 1, but potentially March 3 (near Crystal), and enough evidence exists that we are not yet ready to remove this problem.  Avoid going into, or underneath open or sparsely treed terrain with large start zones above you. 

    This deep persistent weak layer of facets over a slick crust formed mid-January, and is now buried 6-10+ feet deep. We’ve seen avalanches failing on this layer for well over a month now. Shaded slopes in the alpine may be the most likely areas for one of these to release on Tuesday. The most likely way that an avalanche will occur is if a cornice were to fall, or a group of people stood on a shallow spot on the slab. Cornices are large and sagging in some areas, keep on the lookout for these and stay well away from them. 

    (2/27/2021) A deep persistent slab avalanche ran naturally at around 10:30pm on February 26th in a path known as West Camp off Rock Mountain above Highway 2. It filled and expanded the runout zone and the airblast hit the highway. Southeast to Southwest aspects with the crown running from around 6,200ft to 5,400ft.

Avalanche Discussion

On Monday I observed a couple of recent, small wind slabs from alpine terrain on Mount Mastiff, and in White Pine Cirque (see photos below). I could see wind drifting at ridgeline from afar in the morning, and there was lots of wind textured snow at upper elevations. Observers reported shallow reactive wind slabs on Arrowhead on Sunday. 

Last Monday, WSDOT avalanche teams triggered an 8ft deep D3 avalanche on the southeast face of Rock Mountain east of Stevens Pass (our last avalanche known to have failed on the persistent weak layer in this zone). In the Chiwaukum Mountains, a natural D3.5 avalanche in upper-elevation north-facing terrain is suspected to have run on Sunday. A massive avalanche (D4) ran naturally in the West Camp path on Rock Mountain a bit  over a week ago. Viewing the tree-laden debris gives you a taste of the destructive potential of that avalanche as you drive along Highway 2 east of Stevens Pass. The mountains still demand respect because of the potential for these very large avalanches.

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.

Regioni coperte