Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Expect dangerous avalanche conditions as the latest storm adds to the deep snow from the past week. Avalanches will be easy to trigger, they could be very large, and they may run naturally from higher elevations. Avoid being on or under large, steep slopes where avalanches can start or run at middle and upper elevations.

Avalanche problems

  • Storm Slabs

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

    Avalanches could break near the surface, at a number of interfaces in the upper snowpack, or even deeper. You're most likely to trigger avalanches in the recent layers of snow near the surface or where the wind has formed deeper, stiff slabs. Avalanches in wind-drifted snow could be dangerously large and could involve much deeper weak layers. Even smaller slopes and features at lower elevations could be easy to trigger. If enough sun gets through the clouds, avalanches could become easy to trigger in southern aspects.

    Expect another 8-10" of snow near the Cascade crest by the end of Thursday. The new storm slab will build on up to 2ft of storm snow from the past week. Slides that break to deeper layers could be over 4ft deep, widely propagating, and could run long distances downhill. 

    Example very large avalanche from last season.

    Photo: Matt Primomo

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–3

    Stay off of and out from underneath steep slopes at upper elevations. Avalanches may propagate widely and run full path to lower elevations in some areas. Heavy new snow and very strong winds may tip some slopes over the edge on Wednesday. The lowest layer of concern is a crust from early February. Slides that run on this crust could be 4ft deep and propagate widely across terrain features. 

    The eastern half of the range from about Blewett Pass over should receive significantly less snowfall. As such, conditions may be ripe for avalanches, but we may not see the level of activity that we are expecting in the western half and upper valleys.

    An example of a persistent slab in the East Central zone from several years ago. 

    Photo: Jake Larson

Avalanche Discussion

On Wednesday, forecasters went to Blewett Pass and found multiple tests indicating that triggering persistent slab avalanches is likely.  Observers on Dirtyface reported widespread whumphing collapses on a crust/facet sandwich down 2ft. The same layer would propagate with extended column tests. On Monday, the Mission Ridge Pro Patrol reported triggering shallow but widely propagating soft slabs in sheltered pockets during avalanche mitigation work. They reported these slabs failing on recently buried surface hoar. Our snowpack has become complicated throughout intermittent dry spells in February. There are multiple potential weak layers in the snowpack, all the way down to the early February Crust. There are also potential layers of surface hoar and faceted grains from the 11th, 14th, 18th, and the 24th. This incoming storm will act as a good test for these layers.

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