Avalanche forecast

Stevens Pass

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Sunday is shaping up to be a nice day in the hills, but temper that powder panic with some humbleness. Warming temperatures and sun may help to settle the storm snow, but it may also create a more cohesive slab. Avalanches may become easier to trigger, and could fracture in surprising ways if they fail on buried surface hoar, facets, or crusts. 

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Storm slabs may become easier to trigger as the day progresses and temperatures warm. Partial sun and warming temperatures may create a more cohesive slab. Look for signs of instability like cracking and recent avalanches. Slabs could fracture wider than anticipated if they fail on layers of buried surface hoar, facets, and/or a thin crust from earlier in the week. Avalanches could be 1.5-2ft deep, especially in areas that have received wind loading in the past few days, like near ridgelines. Buried surface hoar is 'spatially variable' in that you may find it on some slopes but not others, even if they are the same aspect and/or elevation. With quite a bit of uncertainty, best to keep it reigned in a bit on Sunday and let the storm snow settle out more.

    (12/10/2022)

    A skier triggered slab in the White Pass backcountry believed to have failed on the 12/8 surface hoar layer. This avalanche was 150 feet wide and it's crown was as deep as 2.5 feet. [NNE 6700' HS-ASc-D2-R2-O]

    Photo: White Pass Pro Patrol

Avalanche Discussion

Stevens Pass picked up 0.75" of SWE with about 11" of snow on Saturday. This was somewhat unusual, in that the passes should received less snow and water than areas further east. It's also a somewhat unusual snowpack set up, where a layer of buried surface hoar sits underneath a very thin zipper like 'drizzle crust' from earlier in the week. On Friday, I found a few areas where previous wind drifting had overlaid slabs on this layer. In areas with some wind stiffening, I was able to get fast and clean fracturing. The failure layer often involved buried surface hoar, just underneath the thin crust and was down about 8" then. You can look for surface hoar under the surface on wind-sheltered slopes. This layer could be well over 1.5ft deep on Sunday, especially in areas of heavier wind loading. There's an old saying 'unusual situations can cause unusual avalanches'. This is a good thing to remember as temperatures warm up for the first time in many days on Sunday.

Layers of weak snow and crusts were buried by a series of storms in mid to late November. This layer is now near the ground, and has been observed to be gaining strength and rounding. These older layers generally haven't been a problem for avalanches in this zone as much as in the East Central zone, though it's something to consider after this storm. Remember, the snowpack may be hiding shallowly buried hazards of rocks and stumps, especially at lower elevations. Let us know what you see by submitting an observation!

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