Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Steep slopes near and above treeline are primed for human triggered avalanches, some could be very large and break into old snow near the ground. Tuesday will be a relative lull in the storm pattern, but the snowpack is still adjusting to its heavy new load. Choose conservative terrain, staying off of and out from underneath large open slopes. 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    You could trigger thick and cohesive windslabs in areas exposed to the wind. Look for shooting cracks and other signs of instability such as whumphing collapses or recent avalanches. If a steep open slope appears to have a firm or hollow sounding snow and is near or above treeline, avoid it, and steer clear of going underneath them. Cornices may easily break off and trigger avalanches on the slopes below as well. Any shallower slab in the new snow could break into deeper weak layers in the snowpack, creating a much larger avalanche. There are a number of potential weak layers to be concerned about, so it will be best to stay off of, and out from underneath steep wind loaded slopes. 

    With all the deep new snow, loose dry avalanches may run easily on Tuesday. Look for these fan-shaped slides that start from a point (also known as point releases). In steep terrain, these could entrain lots of snow, and create large avalanches. Roof avalanches may continue into Monday night for towns like Leavenworth, where rain on snow is currently falling.

     

    (1/2/2021) A 240ft wide, 1.5-2ft deep avalanche triggered from a distance by a skier on Saturday 1/2. South aspect at 4,700ft in the Salmon la Sac.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Tuesday is primed for triggering a persistent slab avalanche in the zone. A heavy new slab from Monday's dump is sitting over weak, sugary snow and crusts from early December. Don't trust big, open slopes near and above treeline. Keep your distance from slopes 35 degrees and steeper that are big enough to produce a large avalanche. The most dangerous slopes will be steep, open starting zones, but unsuspecting slopes at mid elevations are candidates for these deep avalanches as well. Look out for obvious signs of instability like recent deep avalanches, whumphing collapses, or shooting cracks. The next couple of days will be a good time to stay off of steep, open slopes as the storms continue to stress these deep weak layers. The Wenatchee Mountains warrant extra caution with such a heavy new load, as the snowpack was previously shallow and fairly weak

    Weak snow above a crust is a tricky and historically deadly weak layer east of the crest. This structure may be anywhere from 1.5ft to 4+ft below the surface, above roughly 5,000ft. In the southern half of the zone, a few potential crust layers exist. In the northern half, weak snow above a crust from early December is more concerning, as the 12/21 crust did not form there. In the Wenatchee Mountains, there is potential for avalanches to run on weak snow near the ground.   

    (12/29/2020) Very large persistent slab avalanche off the East Face of Rampart Mountain i the Entiat Drainage.

Avalanche Discussion

Following a whopping storm on Monday, Tuesday should be a relative break in the prolonged storm and avalanche cycle. Mission Ridge and Leavenworth picked up 1.2" of Snow Water Equivalent, with 9" of dense snow at Mission Ridge. They reported a cycle of natural storm slab avalanches, most running on the old/new interface, but potentially some on older, weak layers. More avalanches likely ran, but we have limited observations so far. A large (D2.5) avalanche was observed on Sunday at 5,400ft in a sparsley treed burn zone near Lake Wenatchee. A D2.5 avalanche was observed from Big Slide Creek in Icicle Creek on Sunday as well. On Saturday, a 240ft wide avalanche was triggered by a skier from a distance at 4,700ft on a South aspect in the Salmon la Sac. Another 200ft wide avalanche was triggered by a snowmobile side-hilling on a SW aspect of Round Mountain that day. These were both about 1.5-2ft deep, and may have run on a recent suncrust. These avalanches may only be deeper and wider on Tuesday.

Before Monday's storm, the snow surfaces consisted of deep, cold snow. Very deep, and low density snow was found on Sunday in the Icicle Creek drainage, where a cycle of large loose avalanches ran recently. Near and above treeline, intense wind loading was occurring during the day, and formed stiffer slabs. 

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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