Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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In sintesi

Deep snowfall accumulations, warming temperatures, and a pre-existing weak snowpack have combined to create very dangerous conditions. Expect the snow to turn heavier and wet, so what was previously low density, fluffy debris on Saturday will become a more powerful wet mass on Sunday. Avoid steep slopes, both large and small while this significant storm rages on.

Problemi valanghivi

  • Storm Slabs

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

    The warming temperatures, continued heavy snow/rain, and strong wind will only create larger and more dangerous avalanches on Sunday. Large avalanche paths could run for the first time this season, with debris potentially filling in tracks and gullies and covering up vegetation that has yet to be covered. Avalanches will likely involve all of the recent snow that has accumulated since Thursday, so these could be well over 3ft deep in places. Heavier snow and warmer temperatures at lower elevations may create upside-down or top heavy slabs, along with difficult travel.

    Despite the stoke for winter and new snow, avoidance of avalanche terrain during these dangerous times is the only rational option. Steer well away from large steep slopes, but also be suspicious of small ones that could push you into buried rocks or creek beds. The shallow coverage beneath the new snow could make for a nasty ride, or deeper burial.

    Example storm slab that was 1.5-3ft deep. Mt Baker Backcountry on Saturday.

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1.5–2

    Warming temperatures and sleet, freezing rain, and eventually rain are expected up to at least 4,500ft. This will change the characteristics of the snow to become wet, sticky, and top heavy. Expect rollerballs and wet loose avalanches to become common as the warm air filters in during the day. Slides may gain mass on continuous steep slopes and create large, chunky debris piles. 

    The timing of the warmup will play a key role in this instability on Sunday. Expect it to happen, and look for signs of wet avalanches which are rollerballs and fresh point release slides. These should clue you into dangerous conditions on slopes of lower elevations. If you see these, then steer clear from steep slopes.

    Example wet loose avalanche from last season.

    Photo: Matt Primomo

Avalanche Discussion

On both Friday and Saturday observers throughout the region have found very reactive instabilities. On Saturday many widespread natural avalanches were reported, along with widespread shooting cracks and whumphing. This is all the bullseye information one could ask for to tell us its just stinkin' dangerous out there. At least one report of a catch and carry with a D2 soft slab came in from the backside of SPMR (little info, but no injuries reported) and I wouldn't be surprised to hear about more. Many of the slides are running on a weak interface including surface hoar and/or facets over a slick crust, and propagating impressive distances across entire features. 

Storm totals as I write are up to 28" with 2.7" of water equivalent. The storm cycle began on Thursday when light, low density snow covered up various weak layers that sat around, rotting for the latter part of November. These include surface hoar sitting directly on a slick rain crust that extents up to at least 6,500ft. The crust itself ranges in thickness and supportability from stout and slick on due south facing slopes, to brittle and decomposed on northerlies. As the storm rages on, these weak layers are waking up. 

Before this week's storm, snow cover was minimal to nonexistent below 4,500ft, especially on sun-exposed slopes. Depending on where you go, the chance to hit buried rocks, logs and other obstacles may still prove a significant hazard. 

You can add to the forecast! Please let us know what you see in the mountains by submitting an observation.

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