Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Sat
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

New snow and wind will cause natural avalanches at upper elevations over the next 24 hours. Weak layers deep in the snowpack could act in surprising ways and produce destructive and unsurvivable avalanches. Avoid open slopes 30 degrees and steeper and stay far away from avalanche path runout zones. 

Problemi valanghivi

  • Wind Slabs

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

    Heavy snowfall and strong westerly winds will build fresh slabs over the next 24 hours. Expect the bulk of precipitation to arrive overnight Thursday with the most dangerous avalanche conditions early morning Friday. Large natural avalanches are very likely near and above treeline on wind loaded slopes 35 degrees and steeper. Expect touchy conditions as new and windblown snow may not bond well to cold, low-density snow from earlier in the week.

    If you venture out Friday, choose simple, low-angle terrain. Avalanches due to new snow and wind could step down and trigger deep weak layers in the snowpack resulting in very large avalanches. Avoid freshly wind-loaded features and anticipate variable loading patterns. Cornices will continue to grow and could drop onto slopes below acting as huge triggers. 

    (1/29/2021) Example of a skier triggered avalanche in wind drifted snow. Photo: Pete Durr

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    A widespread natural avalanche cycle occurred during the storm January 30 - February 2. Numerous avalanches broke 3-4ft+ deep on a layer of weak faceted snow above a firm crust (January 24 interface). Avalanches grew very large (D3), had wide propagation wrapping large terrain features, and ran far distances hitting valley bottoms. A handful of avalanches were human triggered on this layer Wednesday, both in the Excelsior area of Canyon Creek (see photos below) and remotely triggered near Artist Point. Additional loading from new snow and wind will test this layer again 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

Observations continue to trickle in documenting the impressive recent avalanche cycle throughout the West North zone. Avalanches were reported each of the past 11 days, with a heavy loading event (4ft snow, 8.5in water) and several rounds of natural activity January 30- February 2. Many long time locals and professionals reported avalanches in areas they had never seen run, and avalanche paths produce slides larger than they can remember. Several close calls were also reported recently, including natural avalanches running on Mt. Herman's east face hitting Bagley Creek - a high traffic route just a few hundred yards away from the Heather Meadows parking area.

These are unusual and very dangerous conditions. Avalanches related to new snow and wind are concerning enough, and a lingering deep slab instability poses uncertainty and high consequences. Avoid avalanche terrain and be patient while the snowpack takes time to adjust and stabilize. 

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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