Avalanche forecast

East Slopes Central

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Strong winds will create reactive wind slabs at upper elevations. These could step down or run as surprisingly deep and dangerous persistent slab avalanches. Continue to leave a wide buffer between you and wind-loaded slopes at mid and upper elevations.

Avalanche problems

  • Wind Slabs

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

    Very strong winds will create active wind slabs at upper elevations during the day on Thursday. Feel for wind stiffened or hollow sounding snow as you climb in elevation and change aspects.  Any avalanche in the new snow could step down to deeper weaker layers and result in a large and deadly avalanche.  Consider the terrain you're connected to and avoid open wind loaded slopes steeper than 35 degrees. 

    Small loose snow dry avalanches are possible on steep, sheltered slopes.  While these avalanches should be small and predictable, keep them in mind around terrain traps. 

    (2/1/2021) From White Pass on Monday: Example of a small wind slab avalanche stepping down to weaker deeper layers.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    We continue to receive daily confirmation that large persistent slab avalanches are possible at least in the Wenatchee Mountains, but also quite possible in the Icicle, Teanaway, and mountains near Lake Wenatchee.  Snowpack tests and recent human triggered avalanches continue to indicate you can trigger a 1.5-3' slab avalanche above the prominent mid-January crust. Days of snowfall and sustained windy periods have incrementally loaded this facet/crust layer and now avalanches have become difficult to predict, and if triggered could be unmanageable. Slab avalanches may fail on other weak snow layers in the upper snowpack above this crust as well.  When the snowpack is complex, keep your terrain choices simple.  

    Persistent slabs can propagate widely across terrain features and can result in large and deadly avalanches.  Continue to put a healthy buffer between where you travel and large open slopes steeper than 30 degrees.  Stay alert to signs of instability such as recent avalanches, shooting cracks, and whumphing collapses. 

    (2/3/2021) This natural avalanche likely occurred overnight on 02/02. Similar to other slides in the East Central, it failed on facets above the 1/13 crust in non-skier compacted terrain of Crystal Mt. It occurred on a SE aspect at 6500'. Crown depth 2'. Photo: Crystal Mountain Ski Patrol

Avalanche Discussion

Another storm will begin to affect the area on Thursday into Friday. This one won't produce as much snow as recent storms for places like the Wenatchee Mountains, but will favor areas closer to the crest. Almost as important as the amount of new snow coming will be the winds. 

An observer reported a number of large (up to D2.5) avalanches with the recent storm from February 1 or 2 near Holden Village. Mission Ridge Ski Patrol reported a couple of large hard slab avalanches with control work on Wednesday. These likely ran on the crust from 1/13, and were roughly 20" deep x 100ft wide in ridgetop, or near ridgetop terrain. I experienced whumpfing collapses in low angle terrain near the summit of Mt Lillian on Tuesday.  Extended column tests showed propagation was likely about 1.5' down (45 cm) above the 1/13 crust.  Also on Tuesday a 3.5ft deep hard slab was reported by Mission Ridge ski patrol in an unsual location below their ridgeline.  All of these fresh reports build on previous information of human triggered avalanches and widespread collapsing stretching back from last week from the eastern part of the zone including the Icicle drainage, mountains near Leavenworth, and the Wenatchee Mountains.

In all parts of the zone, weak structure can be observed in the top 2-3 feet of the snowpack, and could all result in an avalanche. These include surface hoar and facets resting on a crust beneath the snow that has fallen since Jan 24th, as well as more deeply buried facets sandwiched between weak crusts. At lower elevations, you'll find new snow depth increases, and the recent crust fades away as you increase in elevation.

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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