Bulletin d’avalanche

Stevens Pass

Northwest Avalanche Center
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Danger d’avalanche

Sun
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 2 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Storms have added about 4 feet of snow in the past week. You can trigger avalanches where the wind has formed drifts at middle and upper elevations, and you may even encounter dangerously deep avalanches on older weak layers.  Avoid being on or under large, steep slopes where avalanches can start or run at upper elevations.

Problèmes avalancheux

  • Wind Slabs

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

    You're most likely to trigger avalanches at upper elevations where the wind has drifted the recent snow into stiffer slabs. While winds may be intermittent and from a variety of directions, active blowing snow can clue you into the slopes that are getting loaded. At middle elevations, you can steer around wind-loaded features and slopes over 35 degrees.  However, This isn't a sound strategy at upper elevations. There, conditions are doubly dangerous as there's a chance of triggering very large and destructive avalanches on deeper layers. See more below.

    Take time to test the new snow on inconsequential slopes before traveling in terrain steeper than 30 degrees. Stay off of and well out-from-under steep start zones in wind-loaded terrain and leeward sides of ridges at upper elevations. With all the recent snow, be aware of falling in treewells and keep your partners in sight.

     

    (3/1/2024)

    The crown of a large (D2) natural avalanche that ran in wind drifted storm snow around February 28th.

    Windy Ridge, E, 5,300ft

    Photo: Josh Hirshberg

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

     These avalanches can be very dangerous, difficult to predict, and can give little warning. The best way to manage them is to avoid avalanche terrain where the weak structure exists. Stay off of and far away from steep avalanche paths above 6,000ft. Avoid traveling in areas with complex, overlapping avalanche paths. Avalanches may propagate widely across terrain features, and run full path to lower elevations.

    The heavy snow and wind loading from the last week stressed a weak snowpack structure. At and above 6,000ft, avalanches could break weak layers, including facets above the early February crust, 4-6 feet below the surface. The weak structure is weaker and more prevalent in the eastern portion of the zone. Earlier this week, avalanche workers triggered slides on this layer on shaded aspects and skiers near Lake Wenatchee reported collapses on the same layer. Targeted snowpack tests (compression test, deep tap, propagation saw test) can help you identify the problematic layers. 

     

    (2/28/2024)

    In the neighboring East Central Zone. This remotely triggered avalanche in the Teanaway Drainage failed on facets over the Early February Crust. 

    5600ft, NEE aspectHS-ASr-R3-D2-O

    Photo: Mike Elges

Avalanche Discussion

Since the 24th, the Stevens Pass area has received about 5" of water equivalent, and the snowpack has gained 3-4 feet. The snowpack is slowly adjusting to all of the new weight. 

On Tuesday, multiple observers reported sudden planar test results with compression tests on small faceted grains above the early February Crust. These came in from Grace Lakes and Lanham Lake areas on northerly aspects. Two significant (D2+) natural avalanches were observed from the Camp Chutes off the south side of Rock Mountain on Tuesday. The timing of these is unknown but estimated between the 26-27th. The slides ran down to the bottom of the track (gullies) at least. A wide slab avalanche occurred on a SE aspect at 5,600ft in Highlands Bowl on Monday, this was triggered by a smaller sluff. That same day, control work at SPMR triggered a few avalanches that broke down to the early February Crust.

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