Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A storm just ended and an extreme warming period is about to start, without much of a break from avalanche activity. You can trigger avalanches in wind-drifted snow, but then the sun will start cooking southerly aspects. Avoid steep wind-drifted slopes, and if you notice wet loose activity on sunny slopes, avoid steeper nearby terrain and areas beneath them as well. 

Problemi valanghivi

  • Wind Slabs

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

    You may find brand new or couple-day-old wind slabs during your outing on Thursday. Some slabs could be shallow, only a couple inches deep, whereas others may be a foot or two deep. If you see active signs of wind loading, which may be present along ridgelines at upper elevations, identify where snow is landing and avoid those areas. 

    Snow usually deposits below ridgelines, in gullies or around outcropping and features. Feel for stiffer slabs and search for textured, or rippled snow surfaces. The difference in heaviness may be subtle. You may see long shooting cracks. Steer around slopes greater than 35° where you identify wind loading, as you could trigger an avalanche resulting in a dangerous ride. 

    Example photo: Wind slabs like this could fail on steep slopes with a human-trigger.

  • Loose Wet

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

    Wet loose avalanche activity will pick up midday and you can expect slides to continue until the sun leaves a slope. Freezing levels transition from 3500ft in the morning to an unseasonable 8000ft at the end of the day. The sun will first moisten east-facing slopes a little in the morning, before shifting south and then on to west-facing terrain in the afternoon. As temperatures increase avalanche size will continue growing into the afternoon. 

    You may be able to start the day on sunny aspects, but plan on leaving them as the sun intensifies and wet loose avalanche activity begins. Small rollerballs will be your first indicators before small wet loose avalanches fan out. Slides may become large as the day progresses, digging deeper into all the low-density snow that just fell. When you notice any of this activity, transition to shady aspects or away from any slopes greater than 30° and the runout beneath those slopes as well. 

    Wet loose avalanches may trigger slab avalanches as they pick up mass while traveling down a slope. Make sure you plan your day so you won't have to exit through terrain that earlier did not have avalanche activity but by the end of the day, could be very scary and active.

     

    Example photo: Your first indicator for wet loose avalanche activity is very small rollerballs, before actual wet loose avalanches begin. 

Avalanche Discussion

Neighboring zones have found occasional pockets of a weak surface hoar layer buried beneath the storm snow that began falling on 3/9. It's not out of the question that sheltered locations, which didn't either get wind or see the sun, might harbor pockets of this weak layer, and resulting large avalanches could be triggered. 

The Cascades are heading into a stretch of very warm sunny weather. It will be the first big, spring-like warming event of the year, with high temperatures in the 50’s and freezing levels over 10,000’. Very warm conditions through the weekend could produce significant slab and loose snow avalanches.  As with any warming event, there is a high level of uncertainty as to where, when, or even if this scale of avalanche activity will occur. On the other hand, big natural avalanches aren’t really the kinds of things that should be taken lightly. It’s worth noting that smaller wet loose or wind slab avalanches, cornice falls, or snow shedding from cliffs can provide the trigger needed to pull out a very large avalanche. When planning for the weekend, consider that this is one of the times when an ‘improbable’ avalanche might actually occur.

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