Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Snowpack stability continues to improve. Wind slabs may still be present in above treeline terrain where it may still be possible to trigger one on extreme terrain features. If you experience red flag warning signs such as shooting cracks or whumphs the avalanche danger may be locally elevated and you should seek lower-angle slopes.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    1–2

    We haven't had reports of significant slab instability since temperatures cooled early Monday. However, heavily wind-affected terrain lingers in above treeline terrain. Continue to steer around steep avalanche start zones where cornices and wind-sculpted snow point toward deeper drifts during the last storm cycle. Wind slabs can be triggered up to 5 days after a storm and might be reactive another day or so.

     

     

     

    (12/13/2022)

    Heavily wind-sculpted alpine terrain proved largely unreactive on Mt. Watson. Steep, unsupported slopes nearby should be treated with suspicion on Wednesday.

    Photo: Irene Henninger

Avalanche Discussion

NWAC forecasters and other professionals traveled in north-facing near and above treeline on Mt. Watson. They found heavily wind-affected snow with limited reactivity above treeline. The snowpack was slightly shallower than in the Heather Meadows area but has a similar structure. The 12/8 surface hoar was present and produced a clean shear, but did not produce significant propagation. The 11/25 facet crust combo was also present but was not concerning. The layered snowpack structure has been slower to heal this season given the colder-than-normal temperatures. If you do find evidence of post-storm avalanches, propagating cracks, or whumphs this doesn't align with a low forecast. In this case, you should consider the forecast locally invalid and choose smaller, lower-angle terrain features.

Observers found evidence of high avalanche danger during the last major storm cycle which brought around 40" of snow to Mt. Baker Thursday through Saturday night. Large natural slab avalanches released up to size 2.5 on a variety of aspects around Table Mountain (see photos in the gallery). These slides likely ran on the 11/25 facet crust combo and serve as a reminder that an isolated large avalanche could still be triggered days after a storm on a weaker interface.

In very steep north-facing terrain, cold clear nights may be weakening the upper snowpack (surface hoar was widespread on Mt. Watson). Expect to trigger shallow and potentially faster running dry loose avalanches. On sunny south-facing slopes, adjust your aspect to avoid rollerballs and small wet loose avalanches.

NWAC and the Mt. Baker Pro Patrol regret to pass along news of a fatality involving Snow Immersion and Suffocation (SIS). Unwatched while riding in inbound, extreme terrain, he ended up positioned in deep snow such that he was unable to self-extricate. We offer condolences to everyone directly and indirectly impacted.

Before the storm on Friday, an observer reported triggering a small avalanche in an open meadow below treeline. You can read the observation HERE. The observer found feathery crystals, which were likely surface hoar, below the 40cm thick slab. Surface hoar was also found in a pit dug by a Pro 1 avalanche class in the Baker backcountry at around 5000ft, buried almost 3 feet down on a NE aspect on Sunday. They got a propagating extended column test (ECTP28) result on the layer, indicating that it might take a lot of force for the layer to be affected, but if it fails, it could propagate, resulting in an avalanche. This was found in one pit amidst several they dug. We don't know much about this layer right now, and most information we've gotten from it has been inconsistent. However, several zones are finding this layer, and a few avalanches have been reported as failing on it so far. 

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