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

A steady trickle of snow with a slight bump in winds continue to maintain heightened avalanche danger for mid and upper elevation, exposed terrain. Beware of the potential to trigger two types of slab avalanches; Large, older wind slabs and recently formed soft,  shallow ones. Be ready to back away from steep or unsupported slopes if finding wind stiffened snow, or signs of instability like whumphing collapses.

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. 

    Recent reports of whumphing collapses from northerly aspects near treeline speak to isolated areas of lingering instability with old crust layers. Southerly aspects below treeline have also been active in the adjacent Stevens Pass zone. Steep open, unsupported, and heavily wind loaded slopes may be best avoiding for the time being. Now is a good time to dig quick profiles and hand pits to assess how the recent snow is bonding to these crust layers 1-3ft deep. If you observe any signs of whumphing or shooting cracks, then back off from entering steep slopes nearby. 

    (3/5/2023)

    Cracks in wind-stiffened snow are a sign of wind slab instability. Blewett Pass

    Photo: Matt Primomo

Avalanche Discussion

The cool, cloudy, and showery upslope pattern continues to bring a trickle to a few inches of new snow each day. We expect a slight bump in snow and winds for Wednesday. For the most part, observers have been reporting that the recent snow is soft and uncohesive, but are finding isolated areas of stiffer wind slab. On Monday, observers near the Swath on the western edge of the zone reported whumphing collapses from a north aspect between 5,600ft and 5,800ft. They found the problematic layer down 2.5ft, a decomposing crust, likey from Valentines Day. On Friday an observer triggered a small soft slab on a convex rollover in the upper Icicle Drainage. It ran on a thin recent suncrust (2/25), about a foot down. While these potentially problematic layers may be isolated in distribution, they can produce avalanches as the new snow settles, and gains cohesion. 

The recent soft snow rests over a couple intermittent sun crusts, and a pair of rain crusts from Valentine's Day, which can be found 1-3ft deep. These often present as a crust/facet/crust sandwich, with weaker snow beneath the upper crust. Observations indicate quite a wide variability in the structure of this layer. Observations that point to instability on this layer in the Icicle drainage, and the eastern Highway 2 Corridor so far. One natural slab at 5,900ft on an ENE aspect on Cashmere may have run on it, and a handful of slabs in Stevens Pass zone (see Stevens Pass Forecast Discussion for details) ran  on it. If you get out into the mountains, submit an observation to share what you found.

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