Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

It shouldn’t be difficult to see the wind blowing snow around on Thursday. Once you figure out where the snow is ending up, avoid traveling on those slopes. Give cornices a wide berth and be leery of rocky terrain where you could trigger an avalanche more easily.

Avalanche problems

  • Wind Slabs

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

    Don’t be surprised if your favorite NWAC weather station records gusts over 100mph over the next 48 hours. Winds this strong will easily be able to transport old and new snow to form Wind Slabs on leeward slopes near ridgelines, the sides of gullies, or at the base of cliffs. With such windy conditions, you should be able to notice actively blowing snow to key you into areas to avoid. If the wind has died down temporarily, look for textured snow surfaces or freshly built cornices to help you determine where Wind Slabs may exist. Slabs will be larger and possibly more reactive as you ascend in elevation, and some could break in surprising ways due to some weak snow near the current surface. In wind-sheltered locations or at lower elevations, you could find that Dry Loose avalanches are more prevalent. Use small test slopes to test for slab potential and how the snow is reacting to your weight, regardless of avalanche character and elevation. Avalanches will be easier to trigger on steep slopes over 35 degrees, convexities, or near rocky terrain features.

    (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
    Unlikely
    Size
    3

    Our most recent confirmation of a slide on the Mid-January crust/facet combo is from Tuesday (2/23) when Crystal Mountain Pro Patrol was able to trigger a slide on this layer 5 feet deep and 100 feet wide. On Wednesday, visibility allowed us to look around a bit and we spotted some other large natural crowns in the backcountry near White Pass. Although these slides are not confirmed to have failed on the Mid-January layer, they appear to be deep enough and wide enough that we suspect them to have failed on this layer during the atmospheric river event. The Mid-January crust’s depth will vary across the zone, but measurements from the field near White Pass show this layer is over 7 feet deep. As we roll into another loading event, we’ll further test this layer and see if another round of deep and destructive avalanches occur. Continue to be leery of large open slopes and start zones, especially during periods of rapid loading through wind or precipitation.

    (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 brief break in the weather on Wednesday allowed us to gather some information about the previous storm cycle before turning our mindset toward the next one. The atmospheric river event produced some very large avalanches and left us with a crust (2/23), that becomes less pronounced and more deeply buried (as much as 2 feet has been measured) as you ascend in elevation. On Wednesday, widespread surface hoar was found on northerly aspects near White Pass and could act as a potential weak layer the next few days if the wind doesn’t get to it first. On slopes that saw direct sunshine on Wednesday, some solar-induced avalanches occurred and a new sun crust developed. 

As we start to look forward, the next few days look very windy, and snow should be continuous, with several feet of snow expected by Friday afternoon. So dig your hand pits and use your test slopes to see how reactive the new storm snow is over these crusts. If you ascend in elevation above where the 2/23 crust exists (estimated ~5800’), more recent snow and potential weak layers exist, leading to the possibility of larger avalanches.

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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