Lawinenlagebericht

West Slopes North

Northwest Avalanche Center
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Lawinengefahr

Sat
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

We're quickly switching to cooler temperatures after a very warm Thursday, with the main avalanche concern shifting back to wind drifted pockets of snow. Temperatures will cool as the day progresses, and avalanche danger will increase as snow continues falling. Search for newly drifted wind deposits of heavier snow, and steer around them on steep slopes Friday as it is likely that you could trigger an avalanche on one. 

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    A few inches of snow and strong winds are forecasted overnight. Snowfall during the day amounting to another six inches or so with wind will form wind slabs at mid to upper elevation. As the day progresses, wind slabs will increase in size and become more dangerous, possibly increasing to sizes large enough that triggering one could bury you by the end of the day. Pay attention during your travels, as conditions you find in the morning will likely change as the day progresses. Search for wind slabs around rocky outcroppings, in gullies, and on leeward sides of features. Feel and look for stiffer snow, pillows, or textured surfaces. Moderate to strong winds could mean you'll travel through an area with very little new snow but it might quickly transition to a thicker pocket, possibly a foot or more in depth over a very short distance.

    Thicker pockets, at least 6 inches but probably deeper, are where you might be able to trigger an avalanche. Pay attention to snow cracking from your steps or sled as you travel, as an obvious indicator that the snow is weak. The old snow surface was wet on all aspects and to high elevations Thursday. If the old snow didn't have the chance to cool before the snow began, the new snow layer may stick to the underlying moist layer. If it did cool first, snow may easily slide on the slick underlying crust. The new snow is shallow enough that you can easily dig down with your hand to determine whether the fresh snow layer is sticking well to the underlying layer or not.  If you encounter deeper wind-loaded drifts, especially if poorly bonded, or cracking, steer around nearby steep slopes. 

    Strong winds will increase cornice sizes and load slopes beneath the cornice with wind slabs.  Photo: Pete Durr, USFS Backcountry Ranger 

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1

    Small wet loose avalanches may still occur at lower elevations earlier in the day. However, the incoming cooler temperatures are expected to reduce the likelihood of wet slides as the day progresses. If you're traveling through lower elevation areas and the snow is punchy and you're easily sinking in to your knees or deeper, remain alert for small natural wet loose avalanches or you triggering one on a steep slope. When the surface starts firming up, and isn't as loose and incohesive as the rest of the underlying snow this avalanche problem is probably behind us.

    Brief sun breaks during the day might cause enough warming for new low-density dry snow to begin sending rollerballs down or small wet loose avalanches in steep areas. If you see the sun at all on Thursday, expect to encounter these conditions on south-facing slopes. 

    Rollerballs and wet loose avalanches will mainly exist from Thursday. You might see a few more at lower elevation on Friday.

    Photo: Lee Lazzara

Avalanche Discussion

We didn't receive reports on any large slab avalanches occurring near the bottom of the previous storm snow layer, about 4-5 feet deep, on Thursday, despite a spooky one occurring on Wednesday. Warm temperatures and the wetted and possibly refrozen surface layers are further reducing the chances of large slab avalanches occurring. If you travel to upper elevations, and especially if you don't find an obvious previously wet underlying layer, remain aware of this concern on steep wind-loaded slopes. A human probably couldn't trigger one of these deeper avalanches, but a large, sagging cornice that falls or another smaller avalanche might provide enough weight to trigger a large avalanche. 

This week has been a rollercoaster. Sunday through Tuesday 4-5+ feet of snow fell in the mountains of the West North Zone, and we had some of the best powder snow of the year Tuesday for snowmobilers, skiers and riders, and snowshoers. Tuesday was the day to get out if you're into dry, deep powder because freezing levels skyrocketed to over 9000 feet Thursday. Snow became wet on all aspects and up to every elevation aside from the highest summits. Many wet loose avalanches came down on all steep slopes Thursday. Freezing levels are forecasted to drop to 3500ft by Friday evening and cooler temperatures and snow showers are expected through the weekend and beyond.  This huge variety of weather means snow conditions are variable, with soft wet snow, crusts and some more dry snow to keep travel adventurous on Friday.

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