Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 6 years ago.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

Highlights

Do not ignore the large volume of water and strong winds this storm just delivered to our zone. Avoid wind-drifted piles of snow and slopes over 35 degrees where you could trigger an avalanche more easily. Deeper layers in the snowpack have been showing signs of life and should be taken seriously. 

Avalanche problems

  • Wind Slabs

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

    The wind has been significant throughout the zone recently, moving snow easily to develop Wind Slabs. Look for these slabs on leeward slopes, at the base of cliffs, or on the sides of gullies in any part of the zone, with larger slabs as you ascend in elevation above the previous rain/snow line. The wind has also helped to develop large and dangerous cornices, which may be primed to fall and act as triggers on the slopes below. Taking note of freshly built cornices, textured snow surfaces, or pillow-like piles of snow could help you determine where Wind Slabs may exist. Clues of unstable snow such as shooting cracks and whumpfing collapses as you travel, or feeling hardened snow that seems hollow below your feet, should steer you away from slopes greater than 35 degrees.

    (2/23/2021) This slab was triggered by an intentional cornice drop in Gunsight bowl near White Pass on Tuesday (2/23). The slab was 18" deep. [NE aspect 6300'. SS-ACc-D2-R2-I]

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    On Tuesday, we received word from Crystal Mountain Pro Patrol of a confirmed avalanche on the Mid-January crust that we have been tracking for almost a month. This avalanche released sympathetically to a single explosive, meaning that the avalanche did not occur in the location the explosive was thrown. The slide released 5 feet deep and propagated over 100 feet wide. This is the first confirmed avalanche on this layer in over two weeks in our zone, but we have had other avalanches which we have suspected to have occurred at this interface. This layer has been “waking up” around the Cascades since Sunday and has been suspected to have been the cause of multiple very large avalanches in the Snoqualmie Pass, Stevens Pass, and East Central zones. The depth of this layer varies across the zone, but it may be as deep as 8 feet in some locations. Continue to avoid all large open slopes and start zones. 

    (2/23/2021) This avalanche was released sympathetically during control work by Crystal Mountain Pro Patrol on Tuesday (2/23) and was confirmed to have run on the Mid-January crust/facet combo. [E aspect, 5700'. Photo: Robin Pendry]

Avalanche Discussion

The recent atmospheric river brought fluctuating freezing levels, strong winds, periods of heavy and light precipitation, and mixed precipitation types to our zone. These meteorological factors created plenty of potential failure points in the recent storm snow for avalanches and the snowpack will need time to adjust to the recent load. It also formed a crust below the rain/snow line, which is less pronounced and more deeply buried as you ascend in elevation. This crust could act as a good bed surface for avalanches to run on Wednesday. NWAC forecasters were able to trigger 18” slabs with small cornice drops on test slopes on Tuesday in the White Pass area, and ski patrollers at White Pass reported similar results during control work. With some sunshine in the forecast for Wednesday, look for the recent snow to possibly “slab up” or snow to shed from trees and rocks due to the sun’s influence, possibly triggering loose slides on steeper slopes. At this point, with so much recent snow and wind, multiple weak layers and failure points, and plenty of water in the snowpack, any triggered avalanche is capable of growing large and destructive.

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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