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
2 · Moderato
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In sintesi

Heavy snow will create dangerous avalanche conditions, especially where the wind forms deep drifts at upper elevations. You can trigger avalanches on most slopes steeper than 35 degrees. Stay off of steep, wind-drifted slopes at mid to upper elevations.

Problemi valanghivi

  • Wind Slabs

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

    These avalanches could be big enough to bury or kill you. You can trigger them immediately on the leeward sides of ridges in stiffer slabs and pillows of snow. If you don't see actively blowing snow, stay alert to visual clues that the previous drifting occurred. You may see (or feel) 1) areas of deeper snow near shallower areas, 2) stiffer, wind-sculpted features, and 3) cracks that shoot through the snow. You can avoid getting caught by sticking to slopes under 35 degrees and wind-sheltered terrain

    Expect the strongest winds with heavy snow overnight, though some blowing snow may continue through Wednesday. Wind direction will vary. The cold air temperatures may keep instabilities from gaining strength. Winds slabs will be the most dangerous of today's avalanche flavors. It's best to avoid the areas where you could trigger them.

     

    (11/27/2022)

    Cracking of wind-stiffened slabs near Stevens Pass Mountain Resort.

    Photo: Joe Dellaporta

  • Loose Dry

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

    Loose avalanches will be the biggest and easiest to trigger on wind-sheltered slopes near treeline that are steeper than 35 degrees. Stay alert in steep terrain. These avalanches could push you into a dangerous area if you're not paying attention. You could be injured by hitting shallowly buried logs or other obstacles. If you don't have experience managing these avalanches, it's best to avoid steep terrain. 

    The new snow will generally be cold, light, and dry. It's falling on similarly weak snow.  If the new snow comes in slightly warmer or fast enough, you may be able to trigger more dangerous storm slab avalanches. Use small, inconsequential test slopes and quick snowpack tests to determine if the new snow is cohesive and could break as a slab. 

    (11/20/2020) Small loose dry avalanches from a previous season. Photo: Matt Primomo

Avalanche Discussion

There's a lot of uncertainty with the potent storm that will impact the zone Tuesday night through Wednesday. What we know is the bulk of the snow and wind will come overnight and it will be easy to trigger avalanches. Slight changes in the storm could mean more dangerous avalanche conditions. If you see conditions different than in this forecast, defer to lower-angle terrain.  Unusually cold temperatures will keep most slopes soft and dry. This could also keep storm interfaces reactive longer than normal.

Layers of weak snow and crusts were buried by a series of storms in mid to late November. These have not been a problem for avalanches beyond when they were initially buried. The intense, heavy snow does raise concerns. While unlikely, avalanches could potentially involve deeper weak layers. On Tuesday, observers within the boundaries of Stevens Pass resort found two northerly slopes that harbored weak, larger (1.5mm) facets near the ground. One site produced easy propagating test results (see photos and video below). Last week, an observer found the same layer on similar slopes near Lichtenberg Mountain. Other observations elsewhere report that the layer near the ground has turned to melt forms and is strong.  A slick, older crusts is typically in the upper half of the snowpack. Avalanches could slide on this in previously scoured terrain, where the crust is closer to the surface. Pay attention for whumphing collapses or sugary snow layers near the ground. If you find signs of instability or propagating snowpack tests, stay off of slopes steeper than 35 degrees.

It's still early season, and the snowpack is shallow. Hazards exist such as shallowly buried trees, rocks, and open creeks. Let us know what you see by submitting an observation.

 

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