Bulletin d’avalanche

East Slopes South

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The winds and snowfall tapered. However, triggering avalanches in areas where the wind drifted snow into deep slabs may still be possible on Wednesday. Avoid steep terrain features where you see evidence of large pillow-like drifts that sound hollow or if you observe shooting cracks as you travel. These may be located at lower elevations and on all aspects, particularly near ridges or sparsely treed areas. Bitter cold temperatures will be another hazard to consider on Thursday.

Problèmes avalancheux

  • Wind Slabs

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

    Storm totals from December 20th varied throughout the zone, with some locations picking up over 1 ft of new snow and other locations further east picking up 6 inches or less. The strong, gusty winds were more consistent throughout the zone and drifted snow around even at lower elevations and in places typically more sheltered from winds. Winds and snow continued overnight and into the morning hours of Wednesday. With plenty of cold, dry snow available for transport, there is now likely a wide distribution of wind slabs. You can still trigger these slabs as they continue to settle out. With the strong winds, you could find these slabs in unusual locations and on all aspects. Feel for harder snow layers over softer layers. If you observe long shooting cracks or find hollow sounding pillows of snow, you are traveling on or near a wind slab. You should identify these wind loaded areas and steer around steep terrain features where you find them. 

    In some locations, this new snow fell on weak, faceted crystals or surface hoar, and you may be able to trigger an avalanche in sheltered terrain where you find this weak older snow. For example, on Wednesday, White Pass Ski Patrol triggered an avalanche that propagated widely on this layer. Use quick hand pits to observe how well the new snow has bonded to the old snow surface. If the new snow easily slides off, you should dial down your terrain choices to lower angle slopes.

    (12/20/2022)

    Remotely triggered wind slab near Blewett Pass on December 20th

Avalanche Discussion

As the skies clear and you venture out into new terrain, be aware that conditions may still be touchy in certain terrain. In some locations, you may still be able to trigger lingering storm slabs where over a foot of new snow rests on weak, sugary faceted snow or surface hoar. In other areas, you could find a more favorable snowpack setup. After a storm, it is always important to observe how well the new snow bonds to the old snow surface. Jumping, skiing, or snowmobiling over small, steep test slopes is a great way to see if the new snow will slide easily. You may also trigger fast-moving dry loose avalanches in steep terrain. While these typically start small, they can become larger as they move downhill and can easily knock you off your feet in consequential terrain. 

There are limited current observations across the east-south. But adjacent zones have complicated snowpacks, some with multiple persistent weak layers. There may be similar snowpack structures in the East South, so it will be best to give yourself some extra margins of safety with your terrain choices. You should dig down to identify this weak snowpack structure and consider avoiding steep terrain where you find this setup. There is uncertainty with the distribution of these weak layers across the east-south. But we suspect the most likely spot you can trigger a large persistent slab avalanche is on higher elevation slopes facing north, east, and recently wind-loaded. 

Thursday is shaping up to be the coldest day of the season. So make sure to prepare for these unusually cold temperatures with extra warm layers, face shields, and ensure those grip heaters are up and running.

Many lower elevation areas still have a shallow, early season snowpack. Watch for shallowly buried obstacles, such as downed trees, rocks, and open creeks. Tread lightly if you're snowmobiling or skiing around!

Observations have been quite limited across the zone. So if you get out, please let us know what you see by submitting an observation! 

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