Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

6:30am Update: Upgraded to HIGH avalanche danger based on overnight snow totals and convergence bringing continued heavy snow during the morning hours. See Discussion. 

It is likely that you can trigger avalanches in the foot or more of snow that falls Saturday night. A large load will take at least 24 hours to stabilize, and avoiding travel on steep slopes is your best plan for Sunday. Areas where it will be easiest to trigger avalanches are along ridgelines and other locations where wind deposits the snow into thicker, and more reactive drifts.

Problemi valanghivi

  • Storm Slabs

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

    Small natural avalanches are probable overnight as snowfall rates may reach 2-3 inches an hour. During the day, human-triggered avalanches are likely. Most avalanches will fail within the new snow that fell in the last 24 hours. The storm is accompanied by wind, so depending on your location, you may encounter large drifts of thicker snow. Expect the wind-affected areas to be more reactive to a human trigger.  This is especially the case along ridgelines, on leeward slopes, and around rocky outcroppings. 

    During your travels pay attention to variations in snow surface conditions- is the surface light and fluffy, or does it feel firmer as you slightly shifted your terrain? Pay attention to obvious clues such as cracking. If you’re ski/split touring, this is a great day for doing skin-track tests (see media). Although you’re constantly assessing the snowpack as you travel, unless you have experience with snowpack checks and tests, stay off slopes steeper than 35 degrees on Sunday.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1.5–2.5

    Lingering concerns with the persistent weak layer exist as more snow loads on top. Although an avalanche hasn’t been reported on this layer in over a week, nearly two feet of new snow (weight) on top could tip the scales and we might see avalanches on this layer again. The layer exists 1-2 feet below the old snow surface on upper elevation northerly aspects. Add this problem into the equation, and traveling out in these locations in steep terrain with additional new snow is not a good idea on Sunday.

    This facet/crust sandwich may become more reactive as additional snow loads the slope.  Photo: Irene Henninger

Avalanche Discussion

6:30 Update: Most of the original forecast continues to hold true, but at this point, we are expecting to see more widespread large avalanches and naturals are more likely than originally thought. Travel in avalanche terrain is not recommended during periods of HIGH avalanche danger. 

Sunday is a good day to keep bullseye clues, or red flags, in the forefront of your mind. These are the best indicators of when to avoid some or all avalanche terrain. One red flag which is already in the cards for tomorrow is significant recent heavy snowfall. Wind is also a factor. Look out for recent signs of avalanches and unstable snow. Any one of these indicators means there’s probably an increased chance that you’ll encounter avalanches. If you’re traveling to steeper areas, make sure you’ve done your research by using small test slopes, investigated layer bonding, and determined wind slab potential for starters, before heading out onto the slope. 

The return to winter means big changes from the last few weeks. Change your mindset as a result of this, as the avalanche problem, likelihood, and size shifted dramatically overnight. Additional concerns with new snow over the melted-out older layers could mean you’ll find shallowly buried hazards such as trees and creeks. Especially on south-facing slopes you might collide with hard old debris piles cheekily buried under lower density new snow.

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