Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Update 9pm: Unusually Dangerous conditions exist in the mountains around Cle Elum Lake. Unsurvivable persistent slab avalanches may occur spontaneously, or be triggered easily on steep open slopes, especially in that area. The only way to be sure to not trigger these deep avalanches will be to stay off of, and out from underneath steep open slopes where around 3ft of snow rests over facets on a crust. New snow, wind, and very cold temperatures will create touchy wind slabs on Saturday. Expect reactive conditions, as these shallower slabs are forming over widespread weak snow, like surface hoar and surface facets. 

Problemi valanghivi

  • Wind Slabs

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

    Easterly winds have been blowing since Thursday, and look to continue through Saturday. Slabs are getting thicker in exposed locations susceptible to these east winds. Look for these especially in areas near passes and east-west oriented valleys, where the wind gets funneled. Feel for slightly thicker snow, and look for signs of active wind transport such as small plumes near ridgelines. If you find long shooting cracks in drifted snow, stay off of steep slopes nearby. Any avalanche in the new snow could step down to deeper weaker layers and result in a very large and deadly avalanche above 4,500ft. Consider the terrain you're connected to and avoid steep, open wind loaded slopes. 

    (2/11/2021) Long shooting cracks were observed in freshly drifted snow in wind exposed terrain at Stevens pass on Thursday.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    You can trigger wide and surprising avalanches on a weak snow surrounding a crust from mid-January. This tricky layer is already responsible for a number of burials and one fatality. Slabs can be 3ft deep, propagate widely across terrain features, and can result in a deadly avalanche. Stay well out from under any large open slopes steeper than 30 degrees, as they can be triggered from a long distance away or from below. Most likely, you won't get a warning sign of whumphing collapses, or if you do, it is likely to turn into an avalanche. You can check for this weak structure with a pole handle or probe for weak snow above a crust as you travel. Snow pit tests can confirm this instability, but one pit is not enough to be sure of it's absence. Have a look at the recent avalanche occurrences for the types of terrain these slides can happen in.

    Recent activity has been focused near the crest of the East Central Zone, where more recent snow has piled up. The Salmon la Sac, Teanaway, Icicle, and other areas on the south and western edge of the zone have been favored for recent snowfall and wind, and have the most recent avalanches on this layer. Northwest to Southeast aspects in terrain near or above treeline has been the most likely places to find these. 

    (2/9/2021) Persistent slab avalanches that may have run naturally on an east aspect at around 4900ft in the Knox Creek drainage above Cle Elum Lake. These are suspected to have run on the mid-January crust later in the storm cycle of Feb 5-9th.

Avalanche Discussion

Very cold temperatures with east flow is squeezing out light snowfall and beginning to add up especially in the south and southwest parts of the zone. The temps are cold enough that any accident or incident holds even higher consequences, as frostbite and hypothermia are a very real hazard. An observer noted hearing loud avalanches near Cooper Lake on Friday. At both Snoqualmie and Stevens Pass on Thursday and Friday, observers noted very reactive, fresh wind slabs. Expect similar conditions in areas of the East Central where easterly wind funnel through gaps and up valley locations. This new snow and freshly drifted snow is covering weak surfaces in the form of near-surface facets, surface hoar, and suncrust. This adds another problem to our already complicated snowpack.

Over the past week, there have been many very large avalanches and avalanche involvements including the following: Natural avalanches may have occurred on February 9th near Stevens Pass and Snoqualmie pass. These were on an East aspect at 5,800ft (Stevens), and a Northeast aspects at 5,000ft (Snoqualmie, see photo below). When very large natural avalanches occur days after the last snowfall, we should take a step back and rethink our confidence in any steep slope.

February 8th-Two snow bike riders were caught and buried by a very large avalanche in the mountains west of Salmon la Sac Sno-Park along Cle Elum Lake (See the short video in the media gallery below). One snow biker was partially buried and was able to dig himself out. The other rider was fully buried and killed. The avalanche (HS-AV-R3-D3-O) occurred on a northeast aspect at 4400 ft in the Knox Creek drainage. Our deepest condolences to the family, friends and community. On Saturday, a D3 avalanche resulted in a full burial with no injuries near the Easton Sno-Park. A natural avalanche on the east aspect of Sixtysix Hundred Ridge in the Icicle drainage was roughly 1500ft wide and ~3ft deep. Second-hand reports of remotely triggered avalanches in the Salmon la Sac came in on Sunday. Other natural avalanches were observed that likely occurred between the 6th and 8th near Van Epps Pass, a southwest aspect at 6,500ft in the Icicle, and a west aspect at 6,100ft near Mt Daniel. 

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources. Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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