Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

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

You may be able to trigger large avalanches near and above treeline where the wind drifted slabs. Expect light precipitation, possibly rain, and warming temperatures Thursday night into Friday. 

Problemi valanghivi

  • Wind Slabs

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

    You can trigger large avalanches on leeward, wind-exposed slopes. Strong southwest winds transported snow and formed slabs on Tuesday night into Wednesday. Avalanches will be larger and easier to trigger above treeline. Signs of wind slab instabilities are shooting cracks, whumphing collapses, and recent slab avalanches on leeward and cross-loaded slopes. Stay off of slopes steeper than 35 degrees where you find deeply drifted snow, wind features, and overhead cornices. Cornices may be large and easy to trigger. If you do get up onto a ridgeline, give these a wide berth as they could break and trigger avalanches below. 

    In addition to slabs on the surface, deeper weak layers exist above 5,000ft in areas with a shallow snowpack, such as the Wenatchee Mountains. While it seems unlikely that you could trigger a persistent slab avalanche, we still have uncertainty at upper elevations. If you are in areas with less than 4 feet of snow on the ground, be prepared to make your own assessment of the snowpack.

    Example of intense wind loading off a ridgeline.

Avalanche Discussion

If you travel in an area where enough rain falls to break down surface crusts, you may be able to trigger small wet avalanches below treeline. While this is unlikely, it could occur near Cle Elum in the Salmon La Sac and Teanaway drainages. Deeper weak layers exist in areas with a shallow snowpack, such as the Wenatchee Mountains. On Thursday, I traveled south of Blewett Pass and found about 2.5-4 feet of snow on the ground with a number of hard crusts over weaker faceted snow from December. Snowpack tests pointed to the potential for triggering avalanches that could propagate widely on the December facets. That said, the overlying stout crusts made triggering avalanches on this weak layer seem unlikely. 

A widespread avalanche cycle occurred on the 12th. Observations have been limited but in adjacent zones, the activity has been well documented. I was on Stevens Pass, on Tuesday and every avalanche path I could see had at least one, if not multiple avalanches in it. On Washington Pass, observers reported avalanches up to D3 in size (big enough to break mature timber and bury cars) including an avalanche that hit a closed portion of Highway 20, below Delancey Ridge. 

From January 11th to 13th a major storm limited travel and observations at upper elevations. Large and destructive avalanches ran, though observations are limited. Backcountry travel has been limited by the intensity of the storm and the amount of recent snow, rain, and wind. All of this leaves much uncertainty, especially around what's happening especially at upper elevations. With uncertainty around the likelihood of avalanches at upper elevations, it's best to approach avalanche terrain cautiously and make conservative terrain choices. 

 

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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