Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

Another round of snowfall with very strong wind will create very dangerous avalanche conditions at upper elevations on Saturday. A number of close calls have occurred with large and often surprising avalanches on a slick crust from mid-January, and avalanches could be 4ft deep in wind affected areas. Travel in avalanche terrain at upper elevations is not recommended, and consider avoiding steep, open slopes below treeline.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    The new snow and strong wind will increase the chances for triggering avalanches 2ft to 4ft deep. Persistent slabs can propagate widely across terrain features and can result in large and deadly avalanches. Travel in or under avalanche terrain at upper elevations is not recommended on Saturday. Stay well out from underneath any large open slopes steeper than 30 degrees, as they can be triggered in surprising ways from below. Be alert to signs of instability such as shooting cracks, and whumphing collapses.

    Recent observations continue to indicate that large, hard slab avalanches can release on a crust from mid-January. These have occurred mainly on Northwest to Southeast aspects above 5,500ft. The Salmon la Sac, Icicle, and other areas on the western edge of the zone are the places that are most likely to be very dangerous on Saturday. The Wenatchee Mountains east of Hwy 97 will continue to have these dangerous conditions as well. When the snowpack is this complex, keep your terrain choices simple. Elevations below 4,500ft may offer significantly lower chances of triggering one of these.

    (2/3/2021) This natural avalanche likely occurred overnight on 02/02. Similar to other slides in the East Central, it failed on facets above the 1/13 crust in non-skier compacted terrain of Crystal Mt. It occurred on a SE aspect at 6500'. Crown depth 2'. Photo: Crystal Mountain Ski Patrol

  • Wind Slabs

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

    Extremely strong winds will transport the snow that falls in all open and exposed terrain on Saturday. Feel for wind stiffened or hollow sounding snow as you enter open terrain, and change aspects.  Any avalanche in the new snow could step down to deeper weaker layers and result in a very large and deadly avalanche above 5,000ft. Consider the terrain you're connected to and avoid steep, open wind loaded slopes. Stay alert to indicators of wind slab such as heavy snow drifting, shooting cracks and whumphing collapses. Small loose snow, or soft slab avalanches are possible on steep, sheltered slopes where more than 8" of new snow falls as well.

    (2/1/2021) From White Pass on Monday: Example of a small wind slab avalanche stepping down to weaker deeper layers.

Avalanche Discussion

Another storm is rolling through the Cascades with some very strong winds along with it. Just as important for avalanche conditions as the new snow will be the extremely strong winds, which can transport snow 10x faster than it can fall out of the sky. The storm will favor areas closer to the crest such as the Salmon la Sac, but won't produce as much snow as last weekend's storms for places like the Wenatchee Mountains. 

Observers reported a natural D2 avalanche on an east aspect at 5,500ft west of Blewett Pass on Friday. This appeared to have run on the deeper crust from mid-January. On Thursday, a snowboarder took a ride with a wind slab at Mission Ridge on a Northwest aspect in the Near Treeline elevation band. Luckily they escaped unharmed. An observer reported a number of large (up to D2.5) avalanches with the recent storm from February 1 or 2 near Holden Village. On Wednesday, Mission Ridge Ski Patrol reported 4 large hard slab avalanches with control work. These likely ran on the crust from 1/13, and were roughly 24"+ deep x 100ft wide in ridgetop, or near ridgetop terrain. Whumphing collapses such as the ones I experienced in low angle terrain near the summit of Mt Lillian on Tuesday continue to tell us that deeper weak layers are primed to avalanche. In all parts of the zone, weak structure can be observed in the top 2-3 feet of the snowpack, and could result in an avalanche. These include facets resting on a crust from mid-January, or a sandwich of crusts from that same time. At lower elevations, you'll find less new snow and a stronger recent rain crust. 

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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