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
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Evaluate the bond of new snow and wind slab layers before moving into steeper terrain. Wind speeds should increase in the afternoon ahead of the next storm and build fresh slabs of wind drifted snow at upper elevations. Avoid steep slopes where you observe active wind loading.

Problemi valanghivi

  • Wind Slabs

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

    Wind transported snow was reported with moderate winds Saturday afternoon with a handful of large wind slab avalanches in exposed terrain. Higher wind speeds Sunday afternoon ahead of a powerful storm will step up transport and slab formation at upper elevations. Older wind slabs from Friday night’s storm could still be in play as well.

    If you trigger a slab it would likely be on a leeward slope just below ridgeline, or on a terrain feature like a convex rollover or gully wall. Look for blowing snow, changes in snow consistency or visual clues like wind-scoured ridgelines and cornices to identify and help you avoid steep slopes holding wind slab.

     

    (12/29/2022)

    Blowing snow and sharp wind lips above a freshly formed wind slab.

    Photo: Dallas Glass

  • Storm Slabs

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

    Up to 2’ of new snow has fallen since Friday morning and slab avalanches were reported from all aspects and elevations. Storm slabs usually bond quickly, especially at moderate temperatures. On the other hand, there was too much avalanche activity to just run with the old “24 hours it’s all good” mindset.

    Take a few minutes to investigate the bond of new snow slabs to what’s below whether it be slick crust, less dense snow, or maybe even a thin layer of facets or surface hoar. Small test slopes can help gauge reactivity and how slabs will respond to the weight of a person. Hand pits might show a stronger layer sliding easily on a weaker layer.Get a feel for the new snow and ease into steeper terrain, especially with consequential features like trees or gullies in the runout.

    (3/11/2023)

    Slab avalanche with wide propagation around a gully in Swift Creek.

    Photo: Pete Durr

Avalanche Discussion

With a transition to warmer temperatures wet loose avalanches are more likely at lower and mid elevations, regardless of the amount of sun. Also, the larger-than-average cornices that formed this winter will start to sag and get primed up to come crashing down and lay waste to anything in their path. Keep track of what is above you be it a large cornice or steep slopes producing rollerballs or other signs of wet avalanche instability. It's up to you to stay out of the way.

Observers in the Baker Backcountry reported numerous natural and human triggered slab avalanches. Though small in size they remained reactive into the afternoon.  Continued snowfall partly filled-in some crowns and bed surfaces by the end of the day.

The Mt. Baker Ski Patrol reported a widespread cycle of natural avalanches in terrain adjacent to the ski area Saturday morning. Avalanche mitigation work produced numerous slab avalanches to D2 in size on all aspects with larger avalanches in heavily wind loaded terrain.  

An unexpected 10-12” of new snow fall overnight around the Baker Backcountry with a bit under 1.0” of precipitation and 18” of new snow since Friday morning. Other parts of the zone picked up similar amounts of new snow. An NWAC Forecaster at Schriebers/Baker NRA reported 10” of new snow at treeline from snowfall overnight but no wind transport was reported at treeline.

An observer on Ruby Mountain found 8" of light density new snow.  The new snow had just enough cohesion to produce soft slab avalanches at the old/new snow interface. The wind was strong enough to transport snow above 6500' and shooting cracks were observed as they climbed into more wind affected terrain.

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