Bulletin d’avalanche

West Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Sat
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The amount of new snow in the forecast is plenty enough to build a round of wind slabs. Look for and avoid steep, freshly wind loaded terrain features.  Anticipate higher avalanche danger if snowfall and/or wind speeds are greater than forecast.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    A weak but cold weather system will bring 4-8” of snow by Friday morning. Forecast wind speeds are not especially strong but still pack the punch to transport snow. If you find more than 8-10" of new snow start looking for unstable slabs on all aspects  - not just wind loaded areas. Wind slabs will be easier to trigger where they form over crust or weak, faceted snow and surface hoar.

    Active wind transport should taper by the morning. Wind affected surfaces could be hidden by a few inches of light snow. Track the depth and stiffness of new snow layers as you gain elevation and switch aspects to help identify areas of wind slab. Look for and test freshly wind drifted features to get a feel for the reactivity of fresh wind slabs. When in doubt just steer around steep wind loaded features on lower angle and well supported terrain. 

    (2/15/2023)

    Small natural and human triggered wind slab pockets can help you identify the wind loading pattern in surrounding terrain.

    Photo: Irene Henninger

Avalanche Discussion

Loose snow avalanches are another consideration for Friday. Light new snow should sluff easily on steep slopes. Afternoon sun breaks might initiate signs of instability like rollerballs and small wet avalanches. 

As the holiday weekend approaches it will have been six days since the last large human triggered avalanche. Four different D2 avalanches (three on Feb 8th and one on Feb 11th) are suspected of failing in a layer of weak facets or graupel buried on the 3rd. Two of these avalanches were either triggered from low on the slope or remotely. Given the time for layer interfaces to bond and also considering the amount of backcountry traffic, it’s unlikely - but not impossible - similar avalanches failing at the same interface will occur. A big load from heavy snowfall, rain, a falling cornice, or a smaller avalanche is more likely to wake up the layer in question.

New snow and wind slabs will form over a variety of surfaces including sun crust, wind packed snow, and patches of surface hoar or small faceted grains. In most areas, the stout rain crust buried in mid-January is found roughly 4’ down with deeper or shallower sites in wind affected terrain. Snowpack testing shows improving stability and backcountry travelers in steep terrain have only produced small, shallow slab avalanches since Sunday.

 

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