Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Dangerous avalanche conditions are present as a storm brings several inches of snow to upper elevations and rain to areas beneath about 5000 feet. A lot of uncertainty exists about how reactive these new snow layers will be. Avoid steep slopes on Tuesday, and steer around lower angle terrain beneath steep slopes as well. 

Problemi valanghivi

  • Storm Slabs

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

    Upper elevations could see a foot of snow by morning,  and stormy weather continuing throughout Tuesday.  Expect heavy, wind-affected snow, with subtle slabs that you are likely to trigger. Most avalanches will probably remain in the new snow layer, a foot or less deep, but there is a small possibility that avalanches could break deeper, taking more of the snow we received in the last week.

    Avalanches could occur in all areas where 6 or more inches of snow accumulates, but they are even more likely in areas where wind deposits snow into thicker, heavier drifts. Your best chance at avoiding avalanches during this storm is to stick to low-angle slopes, away from steep overhead terrain. Find slopes less than 30 degrees, and avoid flat terrain beneath large, steep slopes. 

  • Loose Wet

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

    Rain will absorb into the snowpack at elevations below approximately 5000ft. Wet loose avalanches are most reactive when a dry snowpack encounters rain or warm temperatures for the first time. The sun moistened southerly aspects on Sunday, and many of those areas saw small rollerballs running down steep slopes, breaking up the smooth surfaces and forming a subsequent thin crust. Northerly aspects have not been as affected yet, so you may find those areas more reactive as they receive rain.

      Wet snow makes for challenging travel, especially if enough water absorbs so that you're sinking several feet down into the snow. In areas where these conditions are present, or any wet, sticky surfaces, stay alert for the possibility of wet loose avalanches. If you see rollerballs running down steep slopes, or find signs of recent wet loose avalanches, stay off steep slopes and the areas beneath them. 

    Examples of small rollerballs and a small wet loose avalanche that ran naturally. Photo: Zack McGill 

  • Deep Persistent Slabs

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

    Little is known about this deep persistent slab problem. We do know that a few very large avalanches failing several feet deep occurred in the week between Christmas and New Year's on the Shuksan Arm in the Baker backcountry, with at least one failing on a buried surface hoar layer from the Solstice. Reports of two distant but very large avalanches came in on our one blue-sky day Sunday. One was reported as an easily spottable crown near Mt Chardonnay in the Skagit Range viewed from Heather Meadows. It started at about 6600 feet and propagated wide, across gullies and different aspects. It possibly ran up to 1000 feet. Not much additional information is known, but there it is possible that this avalanche failed on a layer deeper than our new storm layers. As temperatures increase and more weight is added to the snowpack, keep the small chances of this type of very large avalanche occurring in the back of your mind. Consider that large deep slab avalanches from higher terrain could run into lower elevations where otherwise you might not expect to encounter a large avalanche.

Avalanche Discussion

Warm, wet temperatures bring out glide cracks. They usually form on steep, smooth slopes such as smooth rock, grass or low shrubs. One was spotted on Little Alaska in the Baker backcountry starting Saturday. Consider avoiding areas beneath these gaping cracks in the snow, as there is a small chance they could avalanche. 

A lot of uncertainty exists as to how many avalanches we will see in this storm. The heavy nature of the snow could mean that it remains stubborn, staying in place. Lower elevations may have already been affected enough by warm temperatures in the last few days, resulting in absorbing rain without producing avalanches. Conversely, the snowpack could be reactive, producing several large avalanches. Expect danger to increase as more precipitation falls during the day as well. Due to all the unknowns, treat the snowpack with suspicion and travel carefully if you're in the backcountry Tuesday. 

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