Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Another significant storm will cause dangerous conditions to continue. Wet slab avalanches may release, and could be destructive as the snowpack adjusts. The new snow and rain present a challenging and complex situation, so hedge your bets and stick to low angled slopes for the time being. 

Avalanche problems

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    As water creeps deeper into the snowpack, widely propagating slabs may become possible. Buried layers of small facets, surface hoar, and larger facets near the ground could all act as the weak layer for destructive wet slab avalanches. You may be able to trigger wet loose slides that entrain deeper snow and become large as well. In many areas, you might just find challenging travel with deep mushy snow, a breakable crust, or a stout and slick rain crust.

    The current conditions are a bit unusual, and wet slabs are tricky to predict, so give yourself an extra margin of safety with your travels. This means steering well out from underneath large, steep slopes while the snowpack adjusts. Look for recent avalanche activity as the number one bullseye of instability information. Wet, mushy, and unsupportable snow are also good indicators that wet avalanches are possible. 

    The same layers that we were previously concerned about with persistent slabs are concerning for wet slabs. See Willie's video below for a great example of this.

    Example of a very large, wet avalanche.

    Photo: Andy Harrington

  • Storm Slabs

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

    New snow should begin to pile up at higher elevations. As it does the temperatures should fluctuating enough to create unstable storm snow. If you brave the elements, look for signs of new snow problems like shooting cracks. Steer around steep slopes during times of heavy snowfall or if you find instabilities. 

Avalanche Discussion

The extent of any recent natural avalanche activity from the recent storms is still unknown with limited obs and likely poor travel. With that said, we could still see natural avalanches occur on Tuesday. Washington Pass picked up about 1.8" of water equivalent since Christmas Eve with about 13" of snow, some sleet, freezing rain, and rain. On Monday temperatures were warm enough for rain and maybe a few inches of snow at Harts Pass, at least. Another slug of moisture arrives Monday night and Tuesday, so expect another round of rain and snow. The current weather makes for a very challenging and complex situation with the snowpack.  An observer found a funky set up in Mazama with air space beneath an ice crust that would collapse with a whumph .On Saturday, Willie reported lots of 6-12" storm slabs east of Washington Pass, and very weak snowpack structure near the ground. Warming temperatures at higher elevations was causing the snow at the surface to become wet, sticky, and more cohesive. Lower elevations had stayed cold with dry snow. 

The mountains close to the Cascade crest have accumulated about 33" of snow since the 20th. Last Tuesday, observers near Cutthroat Lake reported two larger natural slab avalanches likely due to new snow and wind loading. At least one of these may have run on older weak layers around 7,200ft, ENE in Swamp Creek (see photo below).  Observers continue to report lots of collapsing and cracks shooting through the snow in the eastern foothills. On the 18th, an observer triggered a small avalanche on an unsupported northerly feature below treeline in the Silverstar drainage. The slide ran on the mid-November facets. The December 18th interface holds weak grains of small facets, surface hoar, and crusts on southerly aspects. You may be able to find buried surface hoar from December 8th about 2.5 feet below the snow surface.

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