Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

You can still easily trigger freshly wind-drifted slabs of snow on all aspects and even down into lower elevation terrain where you may not typically see wind affected snow. In some sheltered locations, you may also be able to trigger avalanches in the new snow where it rests over a recently buried layer of weak, sugary snow. Sticking to simple, low-angle, low-consequence terrain in wind sheltered areas will be your best bet to avoid getting caught in an avalanche on Wednesday. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    There are up to three persistent weak snow layers in the snowpack, and these small storms have slowly buried these weak sugary snow grains deeper. With this slow, incremental loading, these layers have yet to be tested thoroughly with a large, wet Pacific Northwest storm. The last known sign of instability involving this layer occurred last Thursday when whumping was observed east of Mission Ridge. While they may now be harder to trigger, they are also potentially larger. You should dig down to identify this weak snowpack structure and consider avoiding steep terrain where you find this setup. Be extra vigilant when traveling on northerly aspects with open slopes.

    Stick to lower angle terrain if you observe recent avalanche activity, see shooting cracks under your skis/sled, or hear whumphs.

    (12/10/2022)

    3ft deep persistent slab avalanche in a heavily wind loaded area at Mission Ridge

    Photo: Drew Carlton

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    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 are forecasted to continue overnight and into the morning hours of Wednesday. With plenty of cold, dry snow available for transport, you can expect to find a wide distribution of sensitive wind slabs. You may be able to trigger these slabs in unusual locations and on all aspects. Watch for actively drifting snow along ridges and 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 clear of steep terrain 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. 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. We are just 24hrs out after a very stormy day, so lower angle terrain sheltered from the wind will be your best chance to avoid triggering or being caught in an avalanche.

    (12/20/2022)

    Remotely triggered wind slab near Blewett Pass on December 20th. 

Avalanche Discussion

Tuesday was a proper winter storm with snow and lots of wind. This new snow fell on various surfaces, including weak faceted snow. 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. 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. 

Wednesday will be a frigid day with temperatures down in the single digits, and light to moderate winds will make the wind chill factor something to conder as well. So prepare for these unusually cold temps with extra warm layers, face shields, and ensure those grip heaters are up and running.

Many locations in the East Central zone have a weak snowpack structure with facets formed in mid-November buried near the ground. Most avalanches on these basal facets were on 12/8 and 12/9 and observed from north and east aspects in wind-loaded terrain near Mission Ridge. One very wide avalanche was observed on the 14th in the East North zone near Twisp (see photo below). Further west, observations indicate that the snowpack is deeper, and the weak layers are stronger in the Teanaway and the Salmon La Sac areas.

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