Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

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

Avalanches in wind drifted snow should still factor into your plan for Saturday. Identify where the wind created dense, hollow slabs and bypass these features on softer and less slabby snow. Be prepared for challenging travel on wind affected surfaces in open terrain near and above treeline.

 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    In the northern zones strong north and east winds redistributed loose snow and created a patchwork of eroded old tracks, wind slabs, and other varieties of wind affected snow. Most of the stiff slabs were found to be stubborn to unreactive on test slopes. A few pockets of slab did produce easy, planar results with simple hand shear tests. Some even failed when isolating the column. They should be harder to trigger by Saturday but you could still find one in steep terrain.

    The extent of wind transport and slab development in the Central Cascades is uncertain, but strong winds recorded in the northern zones likely affected a good portion of this portion of the Cascades as well. You may find fewer signs of wind transport farther south in this zone.

    The latest crop of wind slabs should be easy enough to identify and avoid until covered with new snow. Look for smooth, rounded features surrounded by eroded snow surfaces or sun crust. These slabs tend to be hollow and make for challenging travel. There isn’t really much of a reason to be on them. If you do end up in wind loaded terrain, avoid convex or otherwise unsupported terrain features where you are more likely to trigger an avalanche. Larger, ridgeline cornices are currently not reliable visual clues to identify the recent wind loading pattern. This is due to the less common wind direction Thursday.

    (12/16/2022)

    Scoured snow surfaces alternating with pockets of wind slab on a single aspect were observed in the Baker Backcountry on Friday.

     

Avalanche Discussion

No observations from West Central were submitted in the past week. Observers in the neighbor to the north saw signs of the recent wind event nearly everywhere Friday, but no natural or human triggered wind slab avalanches were reported. A few loose wet avalanches on southeast through southwest aspects were noted on more remote peaks. It’s uncertain if these occurred Friday or during prior warming. A crust tops the snow on steep solar slopes but lots of sunny terrain still provides good riding conditions due to the low angle of the sun. Wind protected, shady slopes still offer great snow conditions. 

Also noted was how weak surface hoar and facets at the current surface were flattened or dispersed in wind exposed terrain. While sheltered areas still sport a crop of large surface hoar, most alpine and treeline start zones just saw too much wind for a continuous layer of weak grains to survive. Of course, a few pockets probably made it and could still be an issue when there is a slab above. 

Buried surface hoar and deeper crust-facet layers still lurk in the middle and lower snowpack in some areas. No new avalanches related to either of these layers have been reported this week despite extensive backcountry traffic. Heavy loads might produce a large avalanche in any of these weaker layers that still exist in the snowpack. A big load of new snow or rain from a future storm might also wake up these layers and produce very large natural avalanches.

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