Boletín de aludes

West Slopes North

Northwest Avalanche Center
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Peligro de aludes

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

Lo esencial

Unusual and very dangerous avalanche conditions exist. Additional loading from new snow and wind will only make matters worse on Saturday. Weak layers deep in the snowpack may continue to produce destructive and unsurvivable avalanches. Avoid open slopes 30 degrees and steeper and stay far away from avalanche path runout zones.

Problemas de aludes

  • Storm Slabs

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

    Expect another foot of new snow to accumulate above 3000ft during the day Saturday. Peak instability will likely coincide with the heaviest precipitation rates which look to occur in the afternoon. Natural avalanches due to new snow and wind could grow large, and could even trigger deeper layers in the snowpack as they run downslope resulting in very destructive avalanches. Recent observations indicate a poor bond at the old/new snow interface buried Thursday, and natural and triggered avalanches 6-24in deep propagated widely across terrain features Friday. The problem will only get worse with additional loading over the next 24 hours. Avoid all steep open slopes, and seek out simple terrain away from overhead hazard.

    (2/5/2021) Storm slab avalanche on a northerly aspect near 4800ft outside of the Mt. Baker Ski Area. The avalanche failed 6-8in deep with wide propagation. Photo: Pete Durr, USFS Backcountry Ranger

  • Deep Persistent Slabs

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

    A widespread natural avalanche cycle occurred during the storm January 30 - February 2. Numerous avalanches broke 3-4ft+ deep on a weak layer above a prominent crust (mid-January crust/facets). Avalanches grew very large (D3), had wide propagation wrapping terrain features, and ran far distances hitting valley bottoms. A handful of avalanches were human triggered on this layer Wednesday. Additional loading from new snow and wind will continue to test this layer and may produce another round of destructive avalanches.

    The potential for natural and triggered deep persistent slab avalanches exists above 4000-4500ft on slopes 30 degrees and steeper. This is not a problem to try to outsmart. These conditions are difficult to manage and tricky to accurately assess. You can use snow profiles and snowpack tests to track these layers, but not necessarily as decision-making tools. Build in a wide margin for error and stay away from steep open slopes.

    (2/3/2021) Very large avalanches ran naturally on Mt Herman during the storm cycle between January 31 and February 2.

Avalanche Discussion

The past two weeks were very active in the West North zone with impressive storms, eye-opening avalanche cycles, and a few close calls. Avalanche conditions related to new snow and wind are concerning enough, and a lingering deep slab instability poses uncertainty and high consequences. Avoid avalanche terrain Saturday and be patient while the snowpack takes time to adjust and stabilize.  

Beginning January 24, incremental loads of light snowfall buried a weak old snow surface (mid-January crust/facets) that formed during a prolonged period of cold, clear weather. Observations January 25-29 indicated the old snow surface to be problematic in isolated areas, but avalanches within new and wind drifted snow were more widespread. Heavy loading from new snow and wind January 30 - February 2 (4ft of snow/8.5in water at Heather Meadows) finally pushed the mid-January crust/facets to a tipping point and caused a natural cycle of deep slab avalanches large enough to destroy a house or break mature trees. With clear skies on February 3, many long time locals and professionals were able to document the aftermath, reporting avalanches in areas they had never seen run, and avalanche paths producing slides larger than they can remember. Several close calls also occurred including snowmobile triggered avalanches breaking 3ft+ thick and several hundred feet wide in Canyon Creek on February 3 (photo below), and very large natural avalanches on February 1 on Mt. Herman's east face hitting Bagley Creek with debris and powder clouds running uphill across the valley towards nearby skiers (video below). 

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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