Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Strong winds, additional snow, and recent avalanches warrant a cautious approach on Sunday. Avoid traveling on steep slopes where you suspect the wind deposited snow. Additionally, very large and destructive deep slab avalanches continue to plague the Cascades and should stay on your mind if you choose to enter large avalanche paths.

Avalanche problems

  • Wind Slabs

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

    The winds will continue to shape the snowpack and avalanche hazard around the West South zone for Sunday. Strong westerly winds combined with additional snowfall should from new slabs on top of older firmer wind deposits from the last few days. Consequently, you may trigger small thin new wind slabs or thick deeper older wind slabs from similar terrain. Given any suspected wind-loaded slope greater than 35 degrees a wide berth. You can use clues like blowing snow, cornices, and drifts to help anticipate wind-affected terrain. Instead of tip-toeing around the wind slab, seek out lower angled or less wind-affected areas.

    (2/23/2021) Example: 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

    A pair of very large avalanches (one natural, one explosive triggered) occurred in the Crystal region on Saturday emphasizing the continued presence and potential for the mid-January layer to produce destructive avalanches. These events are not in isolation. Other very large slides occurred near Hwy 20, Hwy 2, and Snoqualmie Pass over the last few days. Let us be very clear, this layer has not gone away and can produce avalanches capable of breaking mature trees and running to valley bottoms. If you choose to enter large avalanche paths, make sure you understand the consequences you and your team are assuming. While triggering a slide on this layer may prove difficult, it could result in a potentially devastating event. Consider staying out of all large avalanche paths including the runouts.

    (2/27/2021) This very large and destructive deep persistent slab was reported by multiple parties on Saturday 2/27. While we don't know exactly when it occurred, it is very recent. E, 6300' 6-8' deep. Union Creek HS-N-D3-R4-O Photo: Joe Hoch

Avalanche Discussion

While most of the precipitation will focus to the north of the area, the West South zone should still receive 2-4” of snow by mid-morning Sunday. This will combine with strong winds and a warming trend. At lower elevations, you could encounter a bit of light rain which produces small loose wet avalanches near the rain-snow line. If you see new rollerballs or find fresh fan-shaped debris, stay away from similar slopes. 

With all the recent snow tracking the potential layers in the snowpack can become challenging. While numerous potential layers and interfaces exist, these three stick out to us. 

  1. 2/25: This interface at the base of the recent storm snow may hold a thin crust or buried surface hoar depending on your aspect and location. If slides fail at this layer, they may triggere easily or propagate widely. 
  2. 2/23: Last week’s atmospheric rive formed and firm layer in the snowpack that may present as a stout curst up to 5800’ While no avalanches have been reported on this layer, it can serve as a simple snowpack marker to help interpret other layers in the snowpack. 
  3. Mid-January: This crust-facet layer continues to lurk in the snowpack. In shallower areas you may find it 6’ (180cm) deep. In many areas, it sits closer to 8-10’ (220-310cm) below the surface. You’ll need a long probe to find this deep persistent weak layer. 

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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