Bulletin d’avalanche

Snoqualmie Pass

Northwest Avalanche Center
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Danger d’avalanche

Tue
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

Monday 0640 Update: Below Treeline raised to Considerable Danger.  With widespread small natural avalanches likely today, avoid slopes 35 degrees and steeper. 

Monday’s wet and wild storm will create dynamic avalanche conditions that may be tricky to manage. Choose terrain that allows you easily reduce your exposure to places where avalanches travel. This includes considering the route you’ll need to take as you return later in the day under very different conditions.

Problèmes avalancheux

  • Storm Slabs

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

    This storm has all the classic ingredients for storm slab avalanches; warming temperatures, significant snowfall, potential weak snow, and moderate winds. These potential avalanches will be your primary concern in the morning. Look for strong over weak layering in the upper snowpack by using hand pits, small slopes, and uptrack tests. When you see these observations crack or fail, you’ve found the upside-down snow. All steep open slopes with more than 6” of new snow should be suspect. If you brave the storm and travel above 4500ft or into wind-exposed areas these slides will likely be much larger. 

    While we don’t expect a widespread natural avalanche cycle Monday, you could see a few slides as some slopes pass their tipping point. This will be most likely during periods of heavy snowfall, as temperatures warm, and when snow transitions to rain.

    (3/13/2022)

    Example: This small slope produced a small avalanche highlighting storm slab conditions. 

    Photo: Alpental Pro Patrol

  • Loose Wet

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

    As the rain-snow line creeps up the mountainsides, so too will wet avalanche problems. So, this will become an issue first in the below treeline band as snow changes to rain at pass level. Fortunately, there isn’t a ton of new snow at these lower elevations, so you’ll likely only find small natural loose wet avalanches. However, conditions will change quickly at mid and upper elevations where more snow and possibly larger avalanches could release. By the end of the day, rain could reach near the tops of the highest peaks. This will result in natural wet loose, and probably a few, wet slab avalanches. While most of these slides should stay small, you could see an isolated large avalanche in big and complex terrain. When you see snow turn to rain, or find natural wet avalanches, dial it back and stay off of and out from under steep slopes.

    (3/3/2022)

    Example: While loose wet slides should be small Monday, in the right terrain, they could become large and dangerous.  

    Photo: Alpental Ski Patrol

Avalanche Discussion

0640 Update: With 6-8" of snow through 6 am in the Below Treeline band, we expect a natural avalanche cycle as conditions warm today.  Small storm slabs and/or wet loose avalanches are likely. 

In some ways, Monday’s weather forecast is complex with lots of dynamic variables. In other ways, it's simple. Significant precipitation, warming temperature, and snow turning to rain will cause conditions to change drastically over short periods of time. With conditions like this, chose plans that give you lots of options to easily identify avalanche terrain and avoid it if needed. There is quite a bit of uncertainty in how much precipitation Snoqualmie could receive Monday. If more water falls than expected, natural avalanches could be larger and more widespread. You’d need to respond by quickly avoiding all avalanche terrain. 

If all these weather factors weren’t enough, the snowpack contains several snow layers that could also fail under the new snow/rain load. A layer of graupel fell during the storm on 3/19. These BB-like grains often produce avalanches even after a storm ends. They may be found just below the snow from the last 24 hrs. Deeper in the snowpack, a layer of weak facets sit over a very thick and stout crust on NW-NE aspects near and above treelines. This layer is likely 3 ft or more deep. So far, only one small avalanche has been reported on this layer in the zone. However, it's hard to say how they’ll react to this additional load. 

At lower elevations travel continues to be difficult. Wet sticky snow, firm rough surfaces, open creeks, and frozen piles avalanches could all make travel challenging.

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