Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Updated 4/10 at 06:30: A Puget Sound Convergence Zone has set up, and continued snowfall with very strong winds will create dangerous conditions through the morning. Avoid steep, wind-loaded slopes at upper elevations, where wind slabs could be over 2ft thick and involve snow from the past few storms. Identify steep slopes to avoid if you find signs of instability such as shooting cracks, and strong over weak layering. Keep your senses awake for signs of surface warming, small wet loose avalanches could be triggered at lower elevations by the end of the day.

Problemi valanghivi

  • Wind Slabs

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

    A Puget Sound Convergence Zone has set up and is deliving heavy snowfall to the pass as of 0600. Continued snowfall with very strong wind and cold temperatures will create active wind slabs through the day on Saturday. The cold temperatures may make for poor bonding of the new snow. Slabs 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. Feel for stiffer snow and identify wind-textured surfaces or pillows of fresh snow. You are most likely to find these below ridgelines, in gullies, and on open slopes or beneath rock bands. If you notice shooting cracks or any fresh avalanches, stay off slopes greater than 35 degrees.

     

    (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.

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1

    Saturday looks like a cold and breezy day, but it's nearly mid-April, so expect some warming of snow surfaces. Loose wet avalanches could be triggered on slopes that receive direct sun, most likely in the afternoon and the eastern part of the zone. Feel for moistening snow surfaces, and watch for indicators of snow surfaces losing strength such as rollerballs. If this starts happening move to shadier slopes or lower angle terrain without steeper slopes above you. 

    (4/9/2021) Small wet loose avalanches ran on steep, east-facing slopes at around 5,500ft in Whitepine Cirque.

Avalanche Discussion

Up to 10" of new snow could fall through the morning on Saturday, adding to the 12" or so that accumulated a few days ago. Cold temperatures and strong wind will easily transport the new snow into drifts and slabs. On Friday, multiple skier triggered avalanches, including an involvement where a skier was caught and carried, occurred in the Snoqualmie Pass zone. This was over 2ft deep, and ran on a layer of graupel over the recent crust on a north aspect at 6,700ft. On Friday, textured and pillowed snow surfaces abounded in upper elevation terrain at Stevens Pass. Observers found that wind slabs could still be triggered on some slopes in the area. Slabs were around a foot thick and more likely to fracture on very steep or unsupported features. 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. 

On Sunday, we can expect the strong mid-April sun will set off another round of wet loose avalanches, similar to what occurred on Friday. The more snow we receive Friday night into Saturday, the larger these may become.

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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