Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Mon
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

On Sunday, large avalanches will be very likely. An intense and dynamic storm will create very dangerous conditions with wet avalanches in the new snow at low elevations and dry slab avalanches above 4,000ft. The best way to stay safe is to stick to slopes less than 30 degrees or avoid backcountry travel altogether.

Problemi valanghivi

  • Storm Slabs

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

    Travel in avalanche terrain at middle and upper elevations is not recommended. Expect large natural avalanches. Be aware of overhead slopes, and don't linger where avalanches could come down from above. Use caution as you approach slopes steeper than 30 degrees. You can avoid triggering avalanches by sticking to lower-angle slopes and steering around steep convexities and rollovers. Recent avalanches and cracks shooting through the snow are "red flag" indicators of the danger. 

    Storm slab avalanche conditions will build rapidly on Saturday night. Above 5,000ft, the snow should remain dry. However, you'll likely find an "upside-down" or strong-over-weak layering in the new snow. The rapid load will stress the underlying recent snow. While avalanches may break within the new snow, some could be 2-3 feet deep.

    (12/11/2021)

    An example of an early season storm slab avalanche at Stevens Pass. 5100ft, SE, Big Chief Mtn

    Photo: Josh Hirshberg

  • Wet Slabs

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

    Wet avalanches can be powerful. Even smaller avalanches will be strong enough to knock you over or push you into trees and rocks. Be aware of the instability, and don't be surprised by the difference in how much more forceful the avalanches will be where you find wet snow. You may be able to trigger wet avalanches on slopes as low as 30 degrees. Similar to the above avalanche problem, identify and avoid steep slopes and typical trigger points such as convexities. 

    Up to about 5,000ft, you could encounter wet avalanches of a couple different forms. The snowpack characteristics may seem more like moist storm snow than the classic water-logged slabs of slush. You may encounter loose avalanches. We have a lot of uncertainty around exactly how these avalanches will behave based on the timing and extent of less frozen precipitation.

    (2/12/2023)

    An example of a very large wet-ish slab avalanche on the south face of Jove Peak from last season.

Avalanche Discussion

Despite how it comes together, Sunday will be very dangerous. I expect Steven Pass to receive 1.5 feet of snow in the overnight hours. Below 5,000ft, precipitation may switch to something less frozen before daylight. By Sunday afternoon, this could be 0.5" rain that percolates into the new snow. Or it could be a wintery mix that forms a soft crust on the surface. Make careful observations of how wet the snow is below the surface and how it behaves.

On Saturday, observers reported over 6" of new snow by dark. The December 6th crust was 1-1.5 feet below the surface. While snow from earlier this week has generally been well-bonded to the crust, avalanches could dig down all the way to the crust.

From  11/30-12/6, the Schmidt Haus weather station recorded nearly 8.5" of water equivalent; over half of that fell as rain starting on the 3rd. Throughout this event, observers reported numerous avalanches of size D1-1.5, with some up to D2. They started as dry slabs and then wet avalanches, with the change to rain on the 3rd. Regardless of whether wet or dry, avalanches were running on the November 30th interface of surface hoar and/or facets over a slick crust. Numerous wet avalanches ran on December 4- 6th, with some running to the ground and entraining dirt. 

If you get out, please let us know what you found by submitting an observation.

Regioni coperte