Bulletin d’avalanche

East Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Sat
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Caution is key coming out of several days of snow and wind, especially at upper elevations.  Assume you can still trigger a large slab avalanche on open slopes below ridgelines where the winds have drifted recent snow.   

Problèmes avalancheux

  • Wind Slabs

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

    You'll need to approach the upper elevations with caution on Friday, getting a lay of the land after several days of wind and snow.  Start with less consequential terrain in areas as you gather visible clues of where winds have drifted recent snow, like fresh pillows and fresh cornices.  You're most likely to trigger a slab avalanche just below lee ridges and other wind-loaded terrain features like at the base of cliffs where spin drifts have accumulated over time. If you encounter red flags like shooting cracks or recent avalanches on similar slopes, step back and choose simpler terrain.  

     

    Wind slab avalanche below ridgeline near Cutthroat Pass from a prior season.

  • Loose Dry

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    Below treeline or in areas with less wind effect, storm totals over the last 2 days are 10-20+", with the highest totals near the crest.  Cold temperatures and less intense snowfall forecast for Thursday night and Friday make it more likely you'll encounter a loose dry avalanche than a storm slab on very steep slopes.  Take stock of the terrain where you could trigger a fast running loose dry avalanche or sluff, and avoid slopes where you could be pushed into a terrain trap like trees or over a cliff band.  

    It's unlikely that you will trigger a storm slab on Friday but they aren't completely out of the picture yet.  In isolated areas, you may find shallow storm slabs lurking on very steep unsupported slopes.  Continue to assess the upper snowpack with quick snow pits or by testing inconsequential slopes.  Surface hoar was reported in valley bottoms in the Washington Pass area prior to this storm cycle.  If you hear audible whumpfs while traveling below treeline, you may encounter avalanches that break wider than expected and are as deep as the two-day storm totals.  In these areas, adjust your terrain selection accordingly by choosing mellower terrain not connected to larger open slopes. 

    (12/23/2021)

    Loose dry avalanches ran easily on steep, wind sheltered slopes near Lake Wenatchee on Thursday.

    Photo: Nate Hough-Snee

Avalanche Discussion

Reports from the Silver Star and Washington pass area on Thursday noted 8" of new snow with 10-20", 2-day totals.  The recent snow was unreactive to quick tests and was generally loose and lacking a slab structure.   It's been several days since we've received direct observations from the upper elevations. Earlier this week observers reported finding surface hoar on Delancey Ridge and in the Hairpin Valley in the typical valley to mid-slope locations.  They also noted steeper S-SW slopes had formed a thin sun crust.  It remains to be seen if these layers warrant more attention over the coming days and weeks with incremental loading events.  Enjoy the relatively moderate temperatures on Friday as we creep towards an arctic blast over the holiday break.  

A widespread avalanche cycle occurred on Saturday, Dec 18th (up to size D2.5) in the Washington Pass area.  A crust buried in early December can now be found roughly 3-5 feet below the surface, especially on slopes near and above 6000 ft.  While avalanches were confirmed on this layer earlier this month, we haven't seen any recent activity and observers continue to log highly variable test results on the crust.    

Régions couvertes