Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Dangerous avalanche conditions are expected to persist through Sunday. The snowpack is ripe for triggering very large avalanches that run on weak snow near the ground. Use extra caution to avoid steep slopes that may harbor weaker old snow layers, ones that have recently received wind loading, and ones that are becoming heavy and wet with warming and sun. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    The new snow is stressing deeper weak layers near the ground. Slopes may be hanging in the balance, just waiting for a trigger to avalanche on Sunday. Reports from Mission Ridge on Saturday were of widespread collapsing and remotely triggered slabs up to 3ft deep. The more new snow you find, the more these deeper weak layers may be getting stressed.

    Steep, northerly aspects are especially vulnerable to avalanching because that's where this layer is weakest, and strong southerly winds on Saturday may have loaded them. Sunday is not a great day to jump into large, steep slopes, especially at upper elevations where slabs are thicker due to wind drifting. Slides could be triggered from below or the edges of a slope in heavily loaded areas. 

    (12/10/2022)

    3ft deep persistent slab avalanche in a heavily wind loaded area at Mission Ridge

    Photo: Drew Carlton

  • Storm Slabs

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

    Soft storm slabs and loose dry avalanches were widespread in areas that received heavy snowfall on Saturday, such as the steep slopes surrounding Leavenworth (Tumwater Canyon/Mountain). The soft storm snow could still fail on lower density layers beneath, on recently buried layers of surface hoar, or even on old weak snow near the ground. Slides may be soft and small in nature, or they could be large and dangerous if they pull out old snow.

    Conditions may remain reactive during the day, or even increase in sensitivity as warm temperatures and some sun may cause the upper layers to become heavier and more cohesive. The consequences of triggering even a small slide may be severe if it steps down and slides on the ground. 

    (11/23/2022)

    A small storm slab on a boulder with a person for perspective.

    Photo: Matt Primomo

Avalanche Discussion

Sunday is shaping up to be a dangerous day because the heavy load of new snow is still stressing weak layers, the warming and sun may create a more cohesive slab, and the call of fresh powder will be something to contend with. Friday night into Saturday a significant upslope storm affected the East Central Zone. Storm totals fell into a fairly wide range, from 0.5" of SWE to 1.4" of SWE. Measured snowfall amounts ranged from 10" (Sasse Ridge) to 20" (Leavenworth). Reports are that Saturday was a good one to steer clear of backcountry avalanche terrain while the storm did it's thing. Three very large avalanches were reported from Mission Ridge, with ~3ft deep crowns. These were easily triggered by the weight of a person, and one was triggered from a distance. WSDOT reported a number of small to large loose avalanches in Tumwater Canyon by 4am Saturday. More surely affected the road while it was closed during the day while heavy snow rates continued. Skiers on Tumwater mountain reported a widespread loose avalanche cycle in the D1-D2 range, depending on the size of the terrain.

It's not quite mid-December and the snowpack is piling up even in the foothills. The cold weather has been a blessing and a curse. Great to have snow on the ground, but the cold temperatures have allowed weak snow near the ground to persist, and in very shallow areas it has grown weaker. Last Thursday, 2-4" of new snow fell and covered up a range of older snow surfaces. This ranged from suncrust on steep southerly aspects, to stiff wind board or soft snow. Surface hoar was also fairly widespread and reported by numerous observers prior, and now may be buried and preserved in a somewhat widespread fashion on open, wind-sheltered slopes.

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