Boletín de aludes

East Slopes Central

Northwest Avalanche Center
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Peligro de aludes

Mon
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 5 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

Strong sun and warming temperatures will create dangerous conditions near the crest where over 10" of new snow may be found. Loose wet avalanches are expected to run on slopes that receive direct sun during the day, so plan to move off of steep slopes once you find signs of warming snow surfaces. At upper elevations you could trigger large wind slabs, be ready to avoid wind-affected snow on steeper slopes. 

Problemas de aludes

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    Although the day will start cold, the strong mid-April sun will quickly warm snow surfaces, and set off a round of wet loose avalanches. The size of these slides will be related to the amount of new snow, and the size of the terrain feature. Slides could be large where more than 10" of snow fell and in larger terrain features. Mountains of the Salmon la Sac, western Stuart Range, and Chiwaukums may hold dangerous conditions on Sunday with more new snow. Look for wet slides to occur first on east-facing slopes, but then on south and west-facing slopes by mid-day. Plan your day to start and end early, and have a contingency plan in place if these begin happening sooner than you anticipate. Feel for moistening snow surfaces, and watch for indicators of warming snow surfaces, such as rollerballs. Be ready to move to shadier slopes, lower angled terrain and avoid going into areas with steeper slopes above you. 

    (4/9/2021) Widespread, large wet loose avalanches off steep southeast aspects at adjacent Stevens Pass. Similar conditions are expected for Sunday for areas near the crest.

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2

    Observers noted plumes of wind blowing snow from afar on Saturday, and wind slabs were reactive in nearby Stevens Pass. Although slabs may become more stubborn to trigger on Sunday, you could still trigger one in the right place. These may break at the new snow/old snow interface, but in prime loading locations they could step down to older layers up to 2ft deep. Expect thicker slabs at upper elevations and on leeward slopes (north to east to south). You are most likely to find these below ridgelines, in gullies, and on open slopes or beneath rock bands. Feel for stiffer snow and look for wind-textured surfaces or pillows. Warming snow surfaces may make for more easily triggered slabs during the day on slopes that receive direct sun. If you notice shooting cracks or strong over weak layering, navigate around or avoid slopes steeper than 35 degrees nearby. 

    (4/9/2021) Cross loaded features on high, north-facing terrain in Whitepine Cirque speak to wind slab potential on those slopes.

Avalanche Discussion

A Puget Sound Convergence Zone set up on Saturday morning, bringing 6-10" of snow for the mountains near the crest. The new snow adds to the 4-8" of new snow that fell on 4/8. Minimal new snow fell in the eastern Wenatchee Range. Very strong winds transported snow through the day on upper elevation terrain, and large plumes could be seen off exposed features. On Friday, multiple skier triggered avalanches, including an involvement where a skier was caught and carried, occurred in the neighboring Snoqualmie Pass zone. This was over 2ft deep, and ran on a layer of graupel over the recent crust on a north aspect at 4,700ft. Textured and pillowed snow surfaces could be found on many upper elevation slopes, and small ski-triggered wind slabs were reported from the Chiwaukum Range. In Whitepine Cirque of nearby Stevens Pass, I found that wind slabs could be up to a foot thick and more likely to fracture on very steep or unsupported features. A wet loose avalanche cycle occurred east of Stevens Pass where more sun made it through the clouds, and the new snow slid easily over the recently buried crust. Avalanches ran on east to south to west aspects at all elevations, and large terrain features produced larger avalanches.

Lower snow totals in eastern portions of the zone may limit avalanche hazard in areas such as the Wenatchee Mountains. The lower snowpack is generally strong and well settled, although a layer of facets associated with a crust from mid-January can be found 2-6 feet below the surface. This layer has been dormant for about a month but it may awaken later this spring with the right conditions.  

If you're out this weekend, help us and the rest of the backcountry community keep up with the quickly changing spring conditions by submitting an observation here. 

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.

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