Bulletin d’avalanche

Stevens Pass

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 6 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Travelers triggered a large persistent slab avalanche at Stevens Pass Wednesday. Another round of stormy weather will only add to this already dicey situation. At mid and upper elevations, dial back your terrain choices and stay off of all slopes greater than 30 degrees.

Problèmes avalancheux

  • Persistent Slabs

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

    Travelers on Wednesday triggered a persistent slab avalanche on Susan Jane Peak near Stevens Pass. The avalanche occurred in wind loaded terrain on a NE aspect at 5450’, was 16” (40cm) deep, and failed on 3mm buried surface hoar. The same party also reported finding buried surface hoar on westerly aspects a few inches above the prominent 12/09 crust. Information like this punctuates several observations from earlier in the week identifying buried surface hoar and facets in the upper snowpack. With more snow expected, any resulting avalanche will only be larger and more dangerous. A common theme among these observations and avalanches seems to be wind stiffened snow. If you travel to mid and upper elevations, give any wind affected slopes greater than 30 degrees a wide berth. Remember, snowpits and snowpack tests can be useful in identifying buried persistent weak layers, however, they can not prove their absence.

    (12/16/2020) This human triggered avalanche occurred on Susan Jane Peak near Stevens Pass. NE aspect 5450' SS-AS-D2-O

  • Storm Slabs

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

    Stormy weather continues to pile up snow around the Pass. Changes in temperatures, wind, and precipitations rate will create several inter-storm layers that may fail and cause avalanches. Steer around any open slopes greater than 35 degrees where you find more than 8” of new storm snow. You can use small slopes and hand pits to see which storm layers fail. However, storm slab avalanche cycles are dynamic and conditions change rapidly. Be leery of applying observations from the moring on slopes you wish to travel in the afternoon. Avalanches may be easiest to trigger during periods of intense snowfall or warming temperatures.

    (12/16/2020) Example Skin track test (up track test) showing cracking in the surface snow. This can indicate storm slabs are present.

Avalanche Discussion

This storm comes as part of an active weather pattern trained on the Pacific Northwest since December 9th. More than 10-20” (25-50cm) of snow now rest above the very prominent 12/09 crust, and this storm will only add to that depth. Any avalanche activity should remain within the upper snowpack above the 12/09 crust. 

At lower elevations, rain and wet heavy snow could produce a few small and isolated loose wet avalanches. The snowpack at these lower elevations has been through and a lot recently, with warm weather and several rounds of rain. As a result, wet avalanche activity should be limited to only a few very steep and rocky slopes. Instead, anticipate areas of thin coverage, open creeks, and shallowly buried obstacles that will require your attention to navigate safely. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

Régions couvertes