Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

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

Warming and strong solar radiation will raise concern for wet loose avalanches. You may also still be able to trigger an avalanche in wind drifted snow at upper elevations. Watch for evidence of recent wind loading near ridgelines and in unsupported terrain, and steer around steep sun-exposed slopes during the heat of the day. 

Avalanche problems

  • Loose Wet

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

    Thursday will bring the warmest temperatures and strongest solar radiation since the storm ended this past weekend. Loose wet activity occurred each day since Monday in nearby zones, but cooler temperatures and cloud cover limited a widespread cycle. Thursday we expect the most wet avalanche activity yet. The sun will first need to break down a melt-freeze crust on solar aspects. By the time this happens, snow surfaces should be wet, weak, and primed for loose wet avalanches. Monitor changing conditions throughout the day, and keep your return routes in mind. The loose wet hazard will be limited early morning and where you find firm and frozen snow surfaces. The best chance for loose wet avalanches will be during the afternoon, especially on south and west aspects. Watch for snow shedding from trees and rocks, and rollerballs and pinwheels following soon after. Although most loose wet avalanches are expected to be small, some could grow large and run far downslope. Steer around steep terrain with evidence of wet snow and move to shaded or lower angled slopes to avoid the problem. 

    (3/9/2021) Rollerballs and pinwheels were already observed in adjacent zones the past few days with filtered sunshine. On Thursday, we expect to see more of these and some actual Wet Loose avalanches due to more sunshine and rising freezing levels. Photo: Enji Cooper

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    You may still be able to trigger an avalanche in wind drifted snow above treeline on slopes 35 degrees and steeper. Of most concern are north-facing convex and unsupported slopes and areas below cornices and rock bands. Several human-triggered wind slabs and a few close calls occurred over the past several days in the adjacent West North Zone. On Saturday a backcountry skier triggered a wind slab avalanche in the West Central near Whitehorse Mountain outside of Darrington.  It was about 10 inches deep, on a north-facing slope at about 4800ft.  You can read the observation here. Fortunately, there were no full burials or injuries. Avalanches in wind drifted snow could break 6in-3ft deep on a variety of mid-storm interfaces or on a crust that formed up to 6000ft on March 4. Continue to approach upper elevation terrain cautiously, and give cornices a wide berth. These unpredictable features are large and overbuilt and can break further back than you may expect or fall onto slopes below acting as huge triggers. Seek out terrain less than 35 degrees where you find recent avalanches, cracking, collapsing, or evidence of wind drifted snow. 

    (3/8/2021) A snowboarder riggered avalanche on Shuksan Arm that broke 1-3ft deep, 200ft wide, and ran 300 vertical feet. The snowboarder dropped the cliff above the slope and triggered the avalanche upon landing. They were caught and carried but remained on the surface with no injuries. Photo: Pete Durr

Avalanche Discussion

From March 4-7, at least 1ft of new snow accumulated above 4000ft throughout the West Central Zone. Deposits of wind-blown snow are now a few days old and becoming isolated and stubborn to trigger. In the adjacent West North Zone, Several human-triggered wind slabs were reported March 6-8, along with natural wet loose activity during periods of sunshine March 8-10. Triggered wind slabs occurred in upper elevation terrain on Shuksan Arm, Table Mountain, and on the south side of Mt. Baker. An impressive icefall avalanche also occurred on Mt. Shuksan's Hanging Glacier on Tuesday (photo below). Be heads up with these transitional spring conditions as ice fall and cornice fall may continue Thursday. Minimize exposure to these and other overhead hazards especially if you venture into the alpine. 

There are dormant layers (mid-January PWL) in our snowpack buried over 10ft deep that produced widespread avalanche cycles and ongoing very large natural avalanches throughout the region for the entire month of February. The adjacent West North Zone was the first to see a major cycle on the layer February 1-2, and isolated but very large natural avalanches as recently as February 25. In the West Central Zone, and in other parts of the region (Stevens, Snoqualmie, West South, East Central) very large and widespread natural cycles on the mid-January layer occurred February 22-25, and as recently as March 1 at Stevens Pass. With quiet weather, no new deep slab avalanches in over a week, and consistent and favorable results in snow profiles and tests, there is enough evidence and confidence to remove the problem from the  West Central forecast for now. Regardless, we will continue to track the Mid-January PWL throughout the region for the remainder of the season. We will not soon forget the very large deep slab avalanches from February, and recognize these types of avalanches are challenging to accurately assess and forecast. It is not out of the question for large triggers like cornice fall to still cause a deep slab avalanche, and a significant weather event may even be enough to reactivate the layer and bring the problem back to life at some point again this season.  

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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