Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

You can still trigger a slab avalanche on slopes steeper than 35 degrees Friday.  Larger avalanches are possible on wind loaded slopes near and above treeline.  Give recently formed cornices a wide berth along ridgelines.  Be wary of loose wet avalanches at lower elevations near terrain traps. 

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    You could trigger slab avalanches within the new snow or at the interface of old and new snow.  If you find snow that slides easily, stick to lower-angle slopes under 35 degrees.  Avoid traveling on convex roll-overs and steep, unsupported slopes. Use extra caution in and around terrain traps, where any avalanche could have serious consequences. Use test slopes or snowpack tests to check how well these slabs are bonding.  Large slab avalanches are possible at upper elevations where recent westerly winds have created deeper slabs on lee aspects. In the Wenatchee range,  only slopes with freshly drifted snow likely present an avalanche hazard. 

    Loose wet avalanches are possible at lower elevations.  If you find yourself sinking in wet snow more than ankle-deep or see natural warning signs like pinwheels or rollerballs releasing from steep slopes, move to lower angle terrain.  Even small loose wet avalanches can knock you off your feet and can cause injury in the wrong piece of terrain.  Also avoid freshly formed cornices along ridgelines, making sure to give them a wide berth.  They are likely to break off with your help and may trigger avalanches on the slopes below. 

    (12/30/2020) A skier triggered a small slab in recent snow. The snow here may have been slightly wind stiffened. 5700ft, west aspect, Salmon la Sac area.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2

    Persistent slab avalanches are still on our radar due to a new load of snow and a weak layer of sugary snow that sits atop an icy crust from back in early December. This structure is similar to that involved in past avalanche accidents in this area and continues to warrant respect. The consequences of triggering avalanches are serious as they could easily bury or kill you. These dangerous and surprising avalanches can catch even the most experienced backcountry travelers. The best way to stay safe is to avoid the type of terrain where you are most likely to trigger one. Keep your distance from slopes 35 degrees and steeper that are open enough and tall enough to produce large avalanches. Watch for obvious signs of instability like recent avalanches, whumphing collapses, or cracks shooting through the snow.

    Look for weak snow just above a thick melt-freeze crust roughly 1.5ft to 3ft below the surface, above 5,000ft. We suspect this is more problematic in the northern half of the zone and closer to the crest where the dry snow exists above these weak layers. The most dangerous slopes will be at the higher elevations, in steep unsupported and rocky terrain. Recent southwest winds may create stiff slabs in some of this terrain. As recently as the 27th observers performed snowpack tests that indicated propagation is still possible with this layer of concern. We found it to 3ft below the surface on an east aspect at 6,600ft in the Near Treeline band near Chickamin Ridge in the Chiwawa Drainage. These layers are not a concern where you find a stout crust near the surface, such as areas further south and at lower elevations. 

    (12/23/2020) A crown of an avalanche that ran between Dec 19-20th on a NE aspect near 7,000ft in the Alpine Lakes Wilderness.

Avalanche Discussion

On Thursday, weather stations just east of the Cascade crest recorded about 10 inches of new snow with about 4" in the Wenatchee Mountains.  The freezing level rose to 4000-5000' later in the day as the heavier precipitation ended. 

On Wednesday, observers in the Salmon la Sac area triggered small reactive slabs during the periods of the heaviest snow and wind. As is typical for the eastern slopes, there is a lot of variability in snowpack depth. Just east of the crest you may find 6ft of snow at 6000ft, but at that same elevation east of Highway 97 in the Wenatchee Mountains, you may only find a few feet of snow on the ground.  As we near the weekend storm cycle, we'll see if significant new loading awakens deeper instabilities in the snowpack. 

And Happy New Year from the Northwest Avalanche Center!  We hope you have a safe and healthy start to 2021. 

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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