Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Expect dangerous conditions as the strong April sun warms snow surfaces and sets off large loose wet avalanches on many slopes. On higher, shaded terrain you could trigger large wind slabs. Sunday will be a good day to give the snowpack time to settle and transition, generally avoiding steeper and more consequential terrain. 

Problemi valanghivi

  • Loose Wet

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

    Although the day will start cold, we can expect the strong mid-April sun to quickly warm snow surfaces, and set off a round of wet loose avalanches. Wet avalanches could run a long distance, and create large debris piles from larger terrain features. Look for these to occur first on east-facing slopes, but then will begin happening on south and west-facing slopes by mid-day. Plan your day to start and end early, and have a contingency plan in place if these begin happening sooner than you anticipate. Feel for moistening snow surfaces, and watch for indicators of warming snow surfaces, such as rollerballs. Be ready to move to shadier slopes, lower angled terrain and avoid going into areas with steeper slopes above you. 

    (4/9/2021) Widespread, large wet loose avalanches off steep southeast aspects on Lichtenberg with very similar conditions to what we can expect on Sunday.

  • Wind Slabs

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

    Observers noted lots of wind-affected snow on Saturday, and although slabs may become more stubborn to trigger on Sunday, you could still trigger a large wind slab. These may break at the new snow/old snow interface, but in prime loading locations they could step down to older layers well over 2ft deep. You are most likely to find these below ridgelines, in gullies, and on open slopes or beneath rock bands. Feel for stiffer snow and look for wind-textured surfaces or pillows. Be aware that a few inches of new snow may be disguising recently formed slabs. Warming snow surfaces may make for more easily triggered slabs during the day on slopes that receive direct sun. If you notice shooting cracks or strong over weak layering, stay off of, or navigate around slopes steeper than 35 degrees nearby. 

    (4/9/2021) Cross loaded features on high, north-facing terrain in Whitepine Cirque speak to wind slab potential on those slopes. The storm on Friday night into Saturday will only add another layer of slab over areas that already look like this.

Avalanche Discussion

A Puget Sound Convergence Zone set up, and delivered around 12" of new snow to Stevens Pass, along with very strong winds on Saturday. This storm adds to the 12" or so that accumulated on the 8th. Observers noted intense wind transport during the day, along with heavy snowfall at times. A small natural wind slab was spotted in near ridgeline terrain off Jim Hill. WSDOT avalanche work produced slab avalanches to large D2's in their west facing paths just west of Stevens Pass. Loose dry avalanches were running easily in the new snow in steep slopes that were sheltered from the winds. On Friday, multiple skier triggered avalanches, including an involvement where a skier was caught and carried, occurred in the nearby Snoqualmie Pass zone. This was over 2ft deep, and ran on a layer of graupel over the recent crust on a north aspect at 4,700ft. Textured and pillowed snow surfaces abounded in upper elevation terrain at Stevens Pass. Slabs were around a foot thick then, but now have another foot or snow of wind slab over them. Also on Friday a wet loose avalanche cycle occurred east of Stevens Pass where more sun made it through the clouds, and the new snow slid easily over the recently buried crust. Avalanches ran on east to south to west aspects at all elevations, and large terrain features produced larger avalanches. 

Beneath the recent storm snow most surfaces are spring melt-freeze layers, aside from upper elevation north aspects where dry snow is present under the new snow. On the southerly half, the top couple feet or more of snow is wet and a few notable crusts are present. 

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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