Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

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

Another few inches of snow and moderate to strong south and easterly winds could create cohesive slabs. These slabs may be reactive to triggering, could be up to a foot thick and result in a surprising avalanche. Identify these through textured surfaces or stiffened snow, and consider steering around steeper or consequential slopes as they'll be fresh on Wednesday.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    As the morning breaks the winds should be just starting to ease. Easterly winds at lower and mid elevations and southerly winds at upper elevations should drift the soft snow from the past few days into deeper areas, scour others, and create cohesive slabs on some slopes. Look for wind textured surfaces or sharp drifts and feel for thicker or stiffer slabs. Look for signs of instability as you gain elevation, especially shooting cracks or recent slab avalanches.

    Small test slopes can be helpful in evaluating instabilities if slabs are less than about a foot deep. Quick hand shears can help to identify weak layers and failure layer characteristics. We expect enough recently drifted snow to create hazard for slab avalanches below ridges, and with cross slope and upslope drifting. Steer around fresh drifts and thick pillows on steeper slopes, or slopes of increased consequences. Slabs could be fairly reactive on Wednesday, as they'll be fresh. In many areas they may also rest on slick crusts, surface hoar, and may result in poor bonding. These conditions could easily result in a surprising slide that propagates fairly wide across the slope. 

    (12/23/2023)

    These textured surfaces are a good indication that wind slabs exist on this slope.

    Photo: Matt Primomo

Avalanche Discussion

Most of the zone picked up another 2-4" of snow on Christmas Day and night, and accumulations since December 21st are in the 5-10" range. Another few inches should fall overnight, and another few going into Wednesday night. The upslope flow should favor upper valleys nearer the Cascade crest. Clouds are expected at mid and upper levels, so visibility shouldn't be quite the same 'bluebird' conditions that many folks enjoyed on Tuesday.

Katie and I traveled to Mission Ridge on Tuesday and found the layer of surface hoar from the solstice to be fairly widespread, and large in some places. It was up to 2cm thick in one profile on a NE aspect at 6,500ft! (see photo below). Wind slabs were on the small side and localized to ridgelines, but nevertheless small ones were reactive. Another observer in the western edge of the zone (upper Icicle) found a more uniform snowpack and largely non-wind affected snow. The sun likely created a thin crust on steeper slopes that face SE-SW.

The recent snow is helping coverage, but can also bury obstacles, leaving them lurking just below the surface. With plenty of brush to contend with off the trails, exposed boulder fields, and rocks on many slopes, consider using summer trails or roads to access higher elevations. 

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