Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

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

Unstable slabs of wind drifted new snow will be found near and above treeline. Steer around wind loaded terrain where you find 6" or more of new snow, shooting cracks, or signs of extensive wind transport like fresh cornices or deep drifts. Expect greater danger during periods of warming.

 

Problemi valanghivi

  • Wind Slabs

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

    With only a few inches of new snow but winds gusting to 50mph, backcountry travelers found plenty of easy to trigger wind slabs that developed between large areas of wind scoured terrain. Sunday should bring more of the same. Winds will remain strong from the south but there is a greater chance of getting 6” or more of new snow overnight. New wind slabs will form and will likely connect across greater stretches of terrain. Additional loading could also wake up a layer of facets that have been found in some areas and make for larger, less predictable avalanches. 

    With strong winds, you might find wind slabs farther downslope and on cross-loaded features in addition to just below ridgeline. Poor visibility or a layer of new snow could make wind slabs harder to pick out in the terrain around you. Monitor new snow depth you as gain elevation and change aspects. Don’t ignore obvious signs of instability like shooting cracks or even subtler clues like a change in snow depth or texture. Evaluate each slope on a case by case basis and travel on lower angle or wind scoured terrain to reduce the likelihood of triggering an avalanche.

    (3/12/2022)

    Skier triggered wind slab avalanche on a west aspect of Table Mt. at ~5000'.

    Photo: Pete Durr

  • Loose Wet

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

    Partly sunny skies and above freezing temperatures could create a round of loose wet avalanches Sunday. With the sun higher in the sky, direct east and west aspects are suspect in addition to the usual south facing areas. Sun-related warming could also make shallow wind slabs and other new snow layers more reactive to triggering. Consider moving off and away from sun-exposed terrain where you see increasing signs of instability like rollerballs, pinwheels, and small avalanches. Also, realize that wind slabs and other new snow layers that seemed unreactive earlier in the day could wake up with a little warming and be more sensitive to human triggers. There is generally not enough new snow below treeline to be reactive with warming. 

    (3/27/2021) A natural wet loose avalanche (D1.5) on a sun-exposed slope in the Baker Backcountry. Photo: Zack McGill 

Avalanche Discussion

A dozen or more wind slab avalanches to D1.5 were reported around the Baker Backcountry in the past two days. On Friday two incidents occurred in which those who triggered avalanches were caught and carried a short distance. Most wind slab avalanches looked to be around 4-8” deep and either released on a firm crust or within layers of wind loaded snow. Some wind loaded features were observed to be more reactive mid-morning Saturday with warming. The wind loading pattern varied widely across terrain with areas of wind slab separated by frozen crust or wind hardened snow, oftentimes with old tracks visible. Unfortunately, the best skiing and riding was also in the terrain where you were most likely to trigger an avalanche. On the other hand, the new wind slabs were at least easy to identify.

New snow and wind slab layers are building on a variety of surface layers including sun crust, dry and weak snow in shady, wind sheltered terrain, old wind slabs, and wind scoured surfaces. Weak, faceted snow continues to be found around the Cascades around the old snow surface buried on March 8th. In some regions, they were found above crust layers from the most recent atmospheric river event in early March. They are more commonly found in shaded terrain but have been observed on most aspects farther south in the Cascades. Besides the snow surface and new wind slab layers, the upper snowpack is generally strong with no current layers of concern. Human triggered avalanches on the Valentine’s Day crust and the late January crust-facet layers continue to be an issue in adjacent regions (East North and the South Coast and Sea-to-Sky zones in Canada). There were no reported avalanches in West North or Central associated with deeper layers since the natural avalanche cycle in late February/early March.

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