Bulletin d’avalanche

West Slopes North

Northwest Avalanche Center
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Danger d’avalanche

Sat
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

Uncertainty exists in terms of how much snow we'll receive Thursday night and during the day Friday. We could see around a foot of snow with moderate to strong winds and more snow continuing throughout the day, and if we are near these numbers then human-triggered avalanches will be likely. Steer around steep slopes which are coated with several inches of new snow, especially if these slopes are wind loaded into thicker deposits. 

Problèmes avalancheux

  • Storm Slabs

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

    Forecasts vary, but we expect enough snow will fall that it will be likely for you to be able to trigger an avalanche on a steep slope.  Old snow surfaces range from smooth wind-blown expanses to textured wind-effect, to crusts. New snow may not stick well to these old, mainly firm surfaces. With a relatively shallow new snow layer this is a time when using small test slopes or hand pits would work well at determining whether there are any weaknesses in the new snow, or at the new snow/old snow interface.   If you find yourself in areas with much more than six inches of new snow coating old snow surfaces, consider steering around slopes greater than 35 degrees. Expect to find steep, wind loaded pockets of snow to be more reactive than non wind-loaded areas. If you notice any recent avalanches, hear whumphing, or see long shooting cracks breaking out from your feet, take these as strong warnings to stay off steep slopes. 

    An example of a D1 slab avalanche which failed beneath the new snow on a steep rollover as I inched out onto the slope. This could be similar to conditions on Friday.  Photo: Irene Henninger

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    Freezing levels are forecasted to be in the 3000-4000ft range overnight and on Friday. Lower reaches of below treeline elevations are expected to see rain, and be moist in general. New snow may be damp at the rain/snowline interface and this snow may rollerball or run in small, wet loose avalanches. The snowline may rise a little throughout the day, so wet loose avalanches may migrate a little higher in elevation as temperatures warm. Any lower-density snow that's been around for a few days may also moisten enough that it could avalanche. These would likely be small, and will probably slide on top of the Christmas crust, less than a foot beneath the surface.  If you see wet loose avalanches or rollerballs running downslope, avoid similar steep slopes, as you could trigger a wet loose avalanche as well. 

    Wet Loose natural avalanches at lower elevations, similar to what you might see on Friday.  

    Photo: ONP rangers

Avalanche Discussion

Our main avalanche concerns are limited to the snow which fell in the last 24 hours or so. There's a small chance that you could trigger an avalanche on an older windslab. Wind has been at the front of our minds since Monday, and we've seen a lot of wind events redistributing snow, as you'll see in the photos below. A few small human-triggered avalanches occurred since Monday, however most of the wind-affected layers remain stubborn. Beneath our most recent round of snowfall, snow surfaces were extremely variable. Occasional pockets of low-density snow that weren't affected by wind were still found in recent days on sheltered north, east and west mid to upper elevation slopes. There are plenty of the previously mentioned wind-affected surfaces. A strong dose of sun on Sunday caused a few wet loose avalanches on steep southerly aspects and now a crust is present on those locations. This south-facing crust will likely get buried to varying extents Friday, although wind may strip areas back down to the crust in some spots. Keep in mind that if snow deposits over this crust, it could act as a good sliding layer for a slab sitting on top of it.  To sum it all up, we expect you'll find at least some new snow on Friday, but conditions could be variable, wind-affected, and damp down low. Be prepared for a variety of conditions and making your own snowpack assessments if you get out. Depending on how much snow and wind we get, avalanche danger could be higher or lower than this forecast. 

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