Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

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

Gusty winds could create shallow slabs of wind drifted snow on less commonly wind loaded aspects. Identify and steer around areas where you see wind loading to reduce the likelihood of triggering an avalanche.

Problemi valanghivi

  • Wind Slabs

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

    Northeast winds will likely form new wind slabs on south and west aspects. These avalanches should be small but easy to trigger as they will be actively building through the morning. New wind slabs may be easy to identify with blowing snow indicating areas of loading. Also, look for scoured ridges with pillowy or lens-shaped drifts on the slope below. If winds are stronger than forecast, anticipate widespread wind slab development and deeper, larger slabs, especially in alpine terrain. 

    Older wind slabs from Saturday’s storm still exist but were observed to be rapidly gaining strength. Despite heavy traffic across West North, no new wind slab avalanches were reported on Monday.

    Track the depth of new snow above the crust as you gain elevation. In wind sheltered terrain there is about 1 foot of new snow over the weak crust buried on Saturday. More than 1 foot over the crust? It’s probably wind loaded. You can use simple tests to evaluate the bond of wind slab layers or simply avoid steep, unsupported terrain which you suspect harbors wind slab.

    On Monday northeast winds scoured snow off this slope which was previously wind loaded. This slope loaded (with southwest winds) during the storm on Saturday. The wind slab avalanche was triggered on Sunday.

     

Avalanche Discussion

In addition to slab avalanches in wind loaded terrain, strong late winter sun could overcome cold temperatures and create instability in the new snow. This could include loose snow avalanches and even the rogue storm slab avalanche releasing in new snow layers. These are most likely to occur in steep, sun exposed terrain around or below cliffs and rocky, treed features. 

Saturday’s storm put down 1-2” of precipitation across West North. Human triggered wind and storm slab avalanches to D1.5 were reported around the Baker BC and also at Schriebers Meadow/Mt. Baker NRA on Sunday. Reported storm slab avalanches mostly occurred in the afternoon as the surface warmed and created a stiffer slab that in turn released on lighter, colder snow below. Small loose snow avalanches, natural and human triggered, were observed on Sunday and Monday. They occurred on both shaded and sun exposed slopes.

Observers in West North found 1' or more of right-side-up new snow above a weak crust buried on February 19th. They found 2-3' in heavily wind loaded, easterly aspects above treeline. The new snow and wind slab layers had become unreactive by Monday in most locations. While sun exposed terrain sported a suncrust first thing in the morning, it had softened by midday despite colder than average temperatures. Crust-facet layering from late January can still be found 3' or deeper in shaded, alpine terrain but no new natural or human triggered avalanches associated with these layers have been reported in the last week.

 

 

 

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