Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

6:45 am UPDATE: Less snow than forecasted, wind slab problem in near treeline elevation band dropped to low danger.  

A slight shift with cooler temperatures and precipitation  Wednesday and Thursday means we've got dry snow avalanche concerns to pay attention to, although recently we've mainly been thinking about spring. Keep an eye out for drifts of thicker new snow at upper elevations, and steer around them in steep areas where a slide could send you into trees or off a cliff, or dump you into a gully.  Very large avalanches on northerly slopes above treeline remain a concern. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    A couple inches of snow Wednesday night and then again during the day Thursday could amount to enough in the upper reaches of near treeline and above treeline areas for you to find wind slabs. This is falling on half an inch of water that came down Monday morning, which was mainly snow at above treeline elevations.  Light to moderate winds could shift the snow into thicker slabs, and possibly make them reactive to a human trigger.

    Search for thicker drifts on leeward ridgelines, around rocky outcroppings, and in gullies. Avalanches in these drifts probably wouldn't be large enough to bury you if you triggered one, but if you're near a terrain trap they could still cause harm. Pay attention to signs of weakness like cracking. Also make note of the new snow in regards to the layers beneath it. These drifts will probably be less than a foot deep, so you could dig down and see whether the snow is sticking well to the underlying layer, or if it easily slides on the old snow surface. Snow that easily slides as a  cohesive slab will be more likely to avalanche. If you find these conditions, steer around slopes greater than 35 degrees.

    You might trigger small wind slabs on steep rolls at upper elevations, like this one earlier this year at Canyon Creek. Photo: Greyson Herdman

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    3

    A layer of faceted snow 4-8 feet deep is likely behind very large avalanches that occurred in the past two weeks. Though you're more likely to encounter a shallow avalanche Thursday, the rare deep slab avalanche will be much more dangerous if you happen to be in the way.  It’s quite unlikely a single person could trigger one of these avalanches but they could still be provoked by a big load like cornice fall, slab, or loose snow avalanche from above. Overall the danger from these is diminishing as colder temperatures make for less cornice fall and other natural activity. That being said it’s still a good idea to not linger on big, northerly alpine slopes below cornices or other hazards.

    (3/29/2022)

    The crown of the large avalanche in the bowl beneath Hidden Lake Lookout. This was triggered by a cornice fall, and likely occurred on the March 8 deep persistent layer.

    Photo: Liza Townsend

Avalanche Discussion

We're currently in a dynamic weather pattern, where periods of cold and snow are reminding us that winter has not yet fully lost its grasp. In many areas, the underlying snow layers remain moist. Despite cloud cover's predominance Thursday, the strong spring sun could tickle out some wet loose avalanches in the afternoon at lower elevation or maybe in the mid-elevation band where a little bit of low density snow fell overnight and during the day. Despite gaining strength from our recent cooling, the overall warmer trend means cornices aren't as strong as they once were. Pay attention to overhead hazards if you're traveling in large terrain, especially in areas where the persistent deep slab remains a concern.  

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