Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Very dangerous avalanche conditions are developing in the mountains. Large to very large natural avalanches may begin to run from higher elevations on Wednesday. Stay off of, and out from underneath large terrain features where slides could run from above. 

Avalanche problems

  • Storm Slabs

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

    We're expecting another foot or two of snow, and it'll come with warming temperatures and very strong wind. The new storm slab will build on 1 to 2ft of weaker, low density from the past few days. Slabs could break within the new snow, at the old snow interface, or any number of layers down to a stout crust from early February. Slides that do break to these deeper layers could be over 4ft deep, widely propagating, and could run long distances downhill. Even small slopes below 5,000ft may present danger, as shallow storm slabs and wet loose slides may run and entrain heavy wet snow at these lower elevations. 

    Stay off of and out from underneath steep slopes on Wednesday. Avalanches could become very large and run through openings in forested terrain.

    Example very large avalanche from last season.

    Photo: Matt Primomo

  • Persistent Slabs

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

    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.

    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. 

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

    Photo: Jake Larson

Avalanche Discussion

Winds and snowfall are ramping up as I write, and we're expecting a lot more storm in the coming day and a half. Snow totals since Sunday are in the 1-2.5ft range across the zone, and stand to double in the next 36 hours. Unfortunatley this time it'll be coming in on a warming trend, which will support natural avalanche activity. Very dangerous conditions are expected to continue through the evening Wednesday and potentially into the day on Thursday.

NWAC 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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