Bulletin d’avalanche

Stevens Pass

Northwest Avalanche Center
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Danger d’avalanche

Tue
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Points saillants

Forecast updated 0730 to reflect higher than expected snow totals and accompanying dangerous conditions at upper elevations.

Following 1.5-2 ft of fresh snow, you can easily trigger an avalanche at upper elevations with the danger greatest at the start of the day.  Ease into the terrain, checking small test slopes to check for mid-storm instabilities. Avoid all upper-elevation slopes steeper than 35 degrees including thicker snow deposits.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Stevens Pass received more snow than surrounding areas, bringing storm totals into the 1.5-2 ft range. We expect that dry loose avalanches on steep slopes will be more frequently encountered, but the greater cause for concern will be mid-storm and new/old storm interfaces that will take time to heal given recent high snowfall rates. Winds early in the storm also created widespread, large, and reactive drifts that may not have healed adding to the challenges at upper elevations, and these slabs may be hidden by less wind-affected snow. It will be difficult to travel safely at upper elevations, so stick to lower slope angles (less than 35 degrees) if you travel at these elevations. Near treeline, you can still trigger avalanches, so use test slopes and frequent hand shears to assess the aforementioned concerns. If you find clean shears or reactive snow, stick to trees and low-angle slopes. Keep in mind that if terrain at lower elevations is more filled in than we anticipate, storm slab concerns will extend below treeline.

    Dry loose may also be a problem in steep terrain approaching 40 degrees. These avalanches could easily knock you off your feet and push you into rocks or stumps that may or may not be submerged under the recent snow.

     

     

    (11/23/2022)

    Example: Storm slab on a steep slope.

    Photo: Matt Primomo

Avalanche Discussion

The snowpack at Stevens Pass elevation has nearly doubled in the past 48 hours, drastically changing the landscape from a few days ago. This means that we're past the depth threshold for avalanche activity in much of the Stevens Pass terrain. Observers on Sunday found that the 12" of snow had widespread wind affects with firm and reactive drifts in near treeline terrain. Additional heavy snow arrived with convergence bands late Sunday and Sunday night.

Recent observations identified weak snow from the long mid-November dry spell, but in most areas near the pass those layers appears to be healing. However, you're most likely to encounter a lingering problem in isolated shady areas. Pay attention for whumphing collapses or sugary snow layers where a problem remains. These locations are most likely to be in more easterly areas of the zone. It's easy to check for this layer with hand pits. If you find sugary, weak snow and a thick slab of snow on top, then avoid slopes steep enough to avalanche nearby.  Since Nov 23 we've seen a variety of snow conditions where the weakness was found in shady and sheltered areas, accompanied by whumphs, whereas other observers reported healing grains and no obvious signs of instability or avalanches. 

As a brief season history up to now, a couple feet of low density snow sat on the ground for a long period of high pressure Nov 8-21. North facing slopes became weak and faceted in the shade. Strong winds and days of sunshine created firm surfaces in many places in the alpine, and slopes exposed to direct sun. Warm temperatures and rain around Thanksgiving may have healed some of the weak layers. Several inches of snow that fell 11/25 in addition to the 12-24" of storm total snow through early Monday all sit on the recent crust (or potential weaker snow previously described).

Despite this last storm,  it's still early season, and the snowpack is shallow. Expect to find around 2-4 ft or snow at mid elevations. Lots of early season hazards exist such as shallowly buried trees, rocks, and other obstacles. In terms of our snowpack, we're still gathering information about what's out there on the ground, so this forecast comes with a fair amount of uncertainty with limited information as a starting point.

 

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