Avalanche forecast

East Slopes North

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 strong winds. 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.

    (12/20/2021)

    Example storm slab avalanche on a small slope.

    Photo: Adam Butterfield

  • Persistent Slabs

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

    Last weekend, strong winds created stiffer slabs that now overly a layer of faceted grains, surface hoar and crusts. The strongest crust at the base was buried in late January. Heavy new snow and strong winds are likely to tip some slopes over the edge to create avalanches that run on these layers.  

    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. 

     

    Example large avalanche that stepped down to a deeper layer.

    Photo: North Cascades Heli

Avalanche Discussion

The mountains are about to get another thick coat of snow! Unfortunately this time it'll come with rising temperatures and potential for natural avalanches. Storm totals since Sunday are in the 8-18" range, and we should pick up another couple of feet by mid day Thursday. Very dangerous conditions are expected to continue through the evening Wednesday and potentially into the day on Thursday.

Observers reported triggering a small avalanche with good propagation on an E aspect at 6,900ft on Tuesday, and a couple of ski triggered slabs up to D1.5 on unsupported rollovers on Monday. A few naturals have been observed, including a wide avalanche beneath cliffs in Blue Lake cirque that appears to have stepped down to a deeper layer. The observers in this drainage found lots of whumphing collapses, and confirmed the instability was on a layer of faceted snow 2ft down above the late January crust.  

Before the recent stormy pattern started on Sunday, observers had been finding weak surfaces including surface hoar and facets, sometimes overlying a thin sun crust. On shady slopes, at mid and upper elevations, there is up to 2.5ft of recent snow over the stronger crust from January 31st. Observers have found a thin layer of weak facets just above this crust. Lower elevations hold substantially less new snow and often don't harbor faceted grains.

Snowpack information is limited outside of the Highway 20 corridor and Harts Pass. Let us know what you find if you get out into the backcountry!

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