Avalanche forecast

East Slopes Central

Northwest Avalanche Center
View on map

Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
Open full map
Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The calendar moves forward but the situation hasn't changed; You can still trigger large and surprising avalanches in the Wenatchee Mountains.  In all parts of the zone, recent strong winds have formed fresh wind slabs and potentially further downslope than usual.  Continue to leave a wide buffer between you and wind-loaded slopes at mid and upper elevations.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    We continue to receive daily confirmation that large persistent slab avalanches are likely in the Wenatchee mountains.  Snowpack tests and recent human triggered avalanches continue to indicate you can trigger a 1-2' slab avalanche above the prominent mid-January crust.  In other parts of the zone,  the likelihood of triggering a persistent slab avalanche in similar wind-loaded terrain may have increased after several days of incremental loading and moderate-strong ridgeline winds.  Persistent slab avalanches may fail on other weak snow layers in the upper snowpack.  When the snowpack is complex, keep your terrain choices simple.  

    Persistent slab avalanches are dangerous and difficult to predict. They 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. 

    Human triggered persistent slab avalanche from earlier in the winter at Stevens Pass.

    Persistent slabs can catch travelers by surprise and propagate widely across terrain features.

  • Wind Slabs

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

    Recent strong W-SW winds have likely formed fresh wind slabs further downslope than usual including shallow wind slabs below treeline.  Feel for wind stiffened or hollow sounding snow as you climb in elevation and change aspects.  In the Wenatchee Mountains, 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 avalanches are possible on steep sunny slopes Wednesday.  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.

Avalanche Discussion

In wind sheltered areas you'll likely find 4-8" of new snow by Wednesday morning across the East Central zone.  Strong W-SW ridgeline winds will finally ease off during the morning hours on Wednesday.  On Monday, rain reached up to 5000-5500' in the East Central zone.  At lower elevations, you'll find a new crust beneath the new snow. 

NWAC professionals experienced whumpfing collapses in low angle terrain near the summit of Mt Lillian.  Extended column tests showed propagation was likely about 1.5' down (45 cm) above the 1/13 crust.  Mission Ridge ski patrol reported a deep but narrow persistent slab avalanche in an usual location below their ridgeline.  All of these fresh reports build on previous information of human triggered avalanches and widespread collapsing stretching back all the way from last week from the eastern part of the zone including the Icicle drainage, mountains near Leavenworth, and the Wenatchee Mountains.

We have less recent observations closer to the Crest but you should be equally suspicious of persistent slab issues in other parts of the zone.  In the top 2-3 feet of the snowpack, there are a number of weak layers that 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. 

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.

Regions covered