Boletín de aludes

East Slopes Central

Northwest Avalanche Center
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Peligro de aludes

Sat
Alta montaña
4 · Fuerte
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Desactualizado: este boletín caducó 6 years ago. Estás viendo condiciones pasadas, no el boletín vigente.

Lo esencial

New snow and very strong wind will increase the chances for very dangerous hard slab avalanches at upper elevations. Slabs could be up to 4ft deep and very wide, or they could be just within the new snow. A number of close calls have occurred in the zone recently, and this combined with another storm should be enough to stay out of avalanche terrain higher in the mountains. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    2–3

    Large persistent slabs continue to be the main concern in the East Central zone and have occurred mainly on Northwest to Southeast aspects above 5,500ft. The Salmon la Sac and other areas on the western edge of the zone boundary will do the best with this storm, and those places are likely to become very dangerous at upper elevations on Friday. The Wenatchee Mountains, Icicle, and mountains near Lake Wenatchee will continue to have these dangerous conditions as well. Snowpack tests and recent human triggered avalanches all indicate you can trigger a 2-4' slab avalanche above the prominent mid-January crust. Days of snowfall and sustained windy periods have incrementally loaded this facet/crust layer and now avalanches have become potentially unmanageable in size. 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.

    Persistent slabs can propagate widely across terrain features and can result in large and deadly avalanches. Put a healthy buffer between where you travel and large open slopes steeper than 30 degrees.  Stay alert to signs of instability such as shooting cracks, and whumphing collapses. 

    (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 montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Very Likely
    Tamaño
    1–2

    Reactive wind slabs were observed on Thursday, and we only expect these to be larger on Friday. Extremely strong winds will continue to transport snow in exposed terrain through Friday. Feel for wind stiffened or hollow sounding snow as you climb in elevation, 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 hard slab 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. This one won't produce as much snow as recent storms for places like the Wenatchee Mountains, but will favor areas closer to the crest. Almost as important for avalanche conditions as the amount of new snow coming will be the winds. 

Observers reported reactive conditions on Thursday with a snowboarder taking a ride in a shallow wind slab at Mission Ridge on a Northwest aspect in the Near Treeline elevation band. 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. I experienced whumpfing collapses in low angle terrain near the summit of Mt Lillian on Tuesday.  Extended column tests showed propagation was likely about 1.5' down (45 cm) above the 1/13 crust. All of these fresh reports build on previous human-triggered avalanches and widespread collapsing stretching back from last week in the eastern part of the zone including the Icicle Creek area and the Wenatchee Mountains.

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 beneath the snow that has fallen since Jan 24th, as well as more deeply buried facets sandwiched between weak crusts. 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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