Avalanche forecast

Stevens Pass

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Isolated chances remain to trigger a large and surprising slab avalanche on crusts buried 2ft deep, even well below treeline. Soft, shallow wind slabs may form during the day with a bump in easterly winds through the pass. Be most leery of any steep, open and unsupported slope exposed to wind drifting.

Avalanche problems

  • Wind Slabs

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

    There's a couple different types of wind slabs you could encounter on Wednesday; Shallow soft slabs, and larger, thicker hard slabs.

    A slight bump in east winds may form shallow, soft but reactive slabs during the day. Watch for wind transport of snow and cracking in surface snow as you gain elevation. Steer around areas that look like fresh drifts. 

    It's the chance of triggering a large old wind slab that could prove fatal. Recent, large avalanche activity has been noted from southerly aspects below treeline, and we have reports of whumphing collapses from northerly aspects near treeline. Steep open, unsupported, and heavily wind loaded slopes may be best avoiding for the time being. It's a good time to dig profiles and hand pits to assess how the recent snow is bonding to older crust layers 1-3ft deep. If you observe any signs of whumphing collapses, or shooting cracks, then back off from entering steep slopes nearby. 

    (3/6/2023)

    A slab avalanche with an unknown trigger likely occurred 3/6 below Skyline Lake. SSW, 4,700ft

    Photo: Josh Hirshberg

Avalanche Discussion

On Tuesday, I went up to investigate a widely propagating, large slab that Josh observed the day prior. This slide appears to have been remotely triggered by a skier as they cut across the top of a slope. It was on a SSW aspect at 4,700ft, well below treeline. On my way up, I found the new snow had variable to fair bonding to the recent sun crust (3/1) about a foot down on some south facing slopes. Deeper down, the Valentines Day Crust sat below two thin sun crusts, and produced propagating test results. See the video below in media gallery. This test was on an adjacent slope to the avalanche, and it likely ran on this same layer, about 2ft deep in places. Instabilities don't appear to be only isolated to southerly aspects though. Observers reported whumphing collapses on north facing slopes from 5,600ft to 5,800ft near the Swath. They identified the layer as a decomposing crust 80cm down, which corresponds to this Valentines Day Crust. 

A small wet loose avalanche cycle occurred on the west side of the pass on Monday (see photo in media gallery below). More sun may shine just west of the pass on Wednesday, so keep a heads up for loose wet slides if the sun does shine for a couple of hours. Rollerballs and moist, sticky snow are all clues for these. A slew of shallow, soft slabs ran over the weekend with a 15" storm day. A few of these likely ran on deeper crust layers.

Last Tuesday the 28th, two larger avalanches were triggered that appear to have run on the more deeply buried crust from Valentines Day. One of these was a large explosive trigger (West at 4,800ft), and another was the third rider on the slope (A heavily wind loaded SE aspect at 5,600ft). These slides were both D2's, and 2-3ft deep. 

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