Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Sun
Alpine
4 · High
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Strong wind will continue to load upper elevation slopes, creating very dangerous avalanche conditions. A complicated and variable snowpack may be nearing a tipping point, and need only the weight of a person to initiate a wide and surprising avalanche. Saturday is a good day to stay off of, and out from underneath steep slopes. Conditions will become more dangerous Saturday evening into Sunday as a major storm makes landfall.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2–3

    In the western half of the zone, we may be reaching a tipping point where it is easy to trigger a large and dangerous avalanche. Persistent slabs dominate the way we travel and plan to travel in the backcountry because all slopes steeper than 30 degrees are suspect. Above 5,000ft, look for a thin layer of weak snow above a crust roughly 14"-24" down from the surface. There may be a layer of buried surface hoar a few inches above this crust as well.

    Another storm overnight Friday with strong wind through the day on Saturday will only add to the stress on these layers. By Saturday these avalanches will be nothing to mess around with.  If you do travel to mid and upper elevations, stay well away from any steep open slope. Listen closely for whumphing, and look for fracturing of large sections of snow. These are direct signs that the snowpack is unstable. Any shallow wind slab that you initiate near the surface could step down to the crust, and become a large and destructive avalanche. Keep it conservative and don't roll the dice with steep slopes near and above treeline.

    (12/18/2020) Part of a D2 persistent slab avalanche that was ~500ft wide and 15"-20" deep in neighboring Stevens Pass zone. The avalanche was unintentionally and remotely triggered by experienced backcountry skiers on 12/17. The avalanche ran on weak snow over the 12/9 crust.

  • Storm Slabs

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

    Another storm will lay down a new layer of snow in the zone. Temperatures are forecast to warm up as it comes in, making for an upside-down feeling snow surface. Steer around any open slopes greater than 35 degrees, and if you find signs of instability such as cracking and small avalanches on steep slopes. Use small slopes and hand pits to see which storm layers may fail. Above 5,000ft, there is potential for any shallow avalanche in the surface layers to step down to the crust and become a much larger slide. 

    (12/17/2020) Long shooting cracks with textured, stiff and wind deposited snow like this one are indicators of wind slab instabilities.

Avalanche Discussion

The active weather pattern continues, and the snowpack is getting deeper with each storm. The storms have been incrementally loading a couple of weak layers that formed during the dry spell of early December. There is a lot of variability with snowpack depth just east of the crest where you may find 6ft of snow at 6000ft, but east of Highway 97 in the Wenatchee mountains you may only find a few feet at the same elevation.  In any case, the December 9th crust is a prominent snowpack marker, and can be found at all elevations up to around 7000ft. Above this layer lies two potential layers of concern, a layer of facets just above the crust, and a thin layer of surface hoar a few inches above that. 

The avalanche danger will vary greatly across the zone on Saturday, with the higher hazard on the west side closer to the Cascade Crest where more snow is expected to fall. In the Wenatchee Mountains near Blewett Pass and the eastern foothills of the Cascades, you may find less dangerous conditions along with less snow.  Expect shallow snow cover at low elevations particularly on low south-facing slopes. We expect very dangerous conditions to continue into the weekend, with a natural avalanche cycle Saturday night into Sunday.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources. Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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