Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

Forecast Update:  Upgraded the Near Treeline elevation band to HIGH due to an increase in forecasted precipitation totals.

A large storm will deposit heavy snow Friday night through Saturday, temperatures will warm and it'll be windy. Avalanches are very likely. Avoid steep slopes, and steer clear of the flatter runout areas beneath avalanche paths. 

Problemi valanghivi

  • Storm Slabs

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

    Slab avalanches are very likely as the storm deposits thick, heavy snow in the area. You could easily trigger an avalanche, and natural avalanches are likely to occur as well. As snow falls through Saturday temperatures will warm, leaving us with an "upside down" snowpack. which leads to heightened avalanche concerns. This means that snow at the surface is thicker and heavier than the snow beneath it. The heavier snow forms a slab that could easily slide on the lighter snow beneath it. Strong winds will redistribute snow at upper elevations into thicker and more reactive slabs also. 

    Feel for a "punchy" snowpack as you step, where heavier snow overlies lighter snow. Watch for obvious clues such as cracking, collapsing, and recent avalanches. The incoming snow may tip the scale on avalanches very quickly, before you even have a chance to register the change.  All these factors taken into account, give avalanche terrain a wide berth on Saturday. You can still get out and play in lower-angle terrain away from large overhead avalanche paths. 

    (12/11/2021) 

    A slab avalanche which occurred last Saturday during the start of our previous storm at Stevens Pass. You will probably see similar avalanches on Saturday.

    Photo: Josh Hirshberg

  • Loose Wet

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

    Warmer temperatures at lower elevations could lead to wet snow conditions. Rollerballs and small loose wet avalanches are likely to occur in the wet snow surface. When you start noticing small rollerballs running down a slope, this may be a precursor to wet loose avalanches. Stay off steep slopes when you notice rollerballs frequently rolling down a slope.

    (3/3/2021) Rollerballs are a good indicator that the snow surface is becoming weak, and wet loose avalanches may follow. Photo: Irene Henninger

Avalanche Discussion

We're getting a lot of water, warming temperatures, and plenty of wind during this storm. Just one of those factors may be enough to cause a spike in avalanche danger, but all three combined definitely makes the alarm bells go off. This is a great recipe for avalanches.  

Several observers on Friday reported that the preexisting snow surface had weak snow crystals, in some places both surface hoar and facets. This means that the new snow layer could have an even easier time sliding on the old snow surface.  On eastern portions of the Stevens Pass zone where the snowpack is colder and shallower, possible weaknesses around the Dec 8 and early December crusts could mean that avalanches in this new snow could step down into these deeper layers, buried a couple feet below the old snow surface. At this time not enough information is known about these layers, so until we know more, keep this in mind. 

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