Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Snowfall is adding up on the eastern slopes. Expect to find some areas with deeper snow, and dry loose avalanches may be triggered and run on steep slopes. As snowfall adds up, our uncertainty surrounding potential to trigger larger slides on deeper weak layers increases. With avalanche danger on the rise, it's a good day to steer clear of large, steep and unsupported slopes at upper elevations.

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 Thursday; 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 and feel for drifts. You could also find reactive slabs in non-wind affected areas, especially steep convex rollovers. Look for cracking in surface snow as you gain elevation, and use hand pits to check how recent snow is bonding to older layers.

    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

  • Loose Dry

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

    Snowfall amounts are likely to be quite variable throughout the zone. If you find an area with deep new snow, then you'll likely be able to initiate small sluffs that run on steep slopes. Dry loose slides tend to occur during, and shortly after steadily accumulating snowfall. 

    Look for signs of instability like fresh fan shaped slides. Test steep slopes before committing to them to see if they'll sluff. Always consider the consequences, especially in larger, steeper, and more consequential terrain.

    An example of small dry loose slides.

    Photo: Katie Warren

Avalanche Discussion

A few inches of snow per day has been the theme. We'll see this start to ramp up over the next two days though, and some favored areas on the east slopes may pick up several inches overnight into Thursday. Heading into Thursday afternoon, things should begin to ramp up further and we expect increasing danger into the overnight period with increased snowfall rates and slightly stronger winds.

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 Wednesday, an observer in the Mission Ridge backcountry found new snow was sluffing on steep slopes. Katie was out in the northern Chiwaukum Range and found about a foot of recent snow that failed cleanly with tilt tests. 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 to be a decomposing crust down 2.5ft, likey from Valentines Day. Last Friday, a small skier triggered soft slab was reported to have run on a recent suncrust, a foot deep in the upper Icicle Drainage. While these potentially problematic layers may be isolated in distribution, they can produce avalanches as the new snow adds up over them 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 wide variability in the structure and depth of this layer throughout the zone. Instabilities have been observed 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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