Lawinenlagebericht

East Slopes Central

Northwest Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
4 · Gross
Waldgrenze
4 · Gross
Unterhalb
3 · Erheblich
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Kernpunkte

Strong wind, warming temperatures, plentiful new snow and a weak pre-existing snowpack have combined to create very dangerous conditions at mid and upper elevations. Expect the snow to turn heavier and wet, so what was previously light, 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.

Lawinenprobleme

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    1.5–2.5

    Strong wind, warming temperatures, and continued snow and rain, will only create larger and more dangerous avalanches on Sunday. Large avalanche paths at upper elevations 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 1.5-2.5ft deep in places. Areas further west in the zone have received deeper storm totals, so slides could be larger there. Further east in the zone, like the Wenatchee Mountains, avalanches may be limited to primarily windloaded terrain. Use quick tests and small slopes to check how easily the new snow slides before traveling near steeper terrain.

    Despite the stoke for winter and new snow, avoidance of avalanche terrain during these dangerous times is the only rational option. Heavier snow and warmer temperatures at lower elevations may create upside-down or top heavy slabs, along with difficult travel conditions. 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. 

    1.5-3ft deep crown in the Mt Baker Backcountry on Saturday.

  • Loose Wet

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1.5–2

    Warming temperatures and sleet, freezing rain, and eventually rain are expected to middle elevations. 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 your localized avalanche danger. Later in the morning and further south and west in the zone we'll see the most drastic warmup, so expect more dangerous conditions there. Areas further east and further north may only see limited rain on snow. In any case look for the signs of wet avalanches which are rollerballs and fresh point release slides to clue you into dangerous conditions on steep slopes at lower elevations. If you see these, then steer clear from steep slopes with continuous snow cover.

    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. We have minimal new observations from the East Central as access has been difficult, but from both Snoqualmie and Stevens Passes 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. 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 ~2.5" of water equivalent with about 2ft of snow at Sasse Ridge and Trinity. Mission Ridge picked up just shy of an inch of water with about a foot of new snow. 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. In areas further east the crust may not exist, or has completely decomposed. In these very shallow eastern parts of the zone you're more likely to find very weak, sandbox like snowpack consisting of mostly faceted grains. As the storm rages on and adds more snow over these layers, we're likely to see them play a part in avalanches.

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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