Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

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

Significant winds will easily load leeward slopes on Thursday. Give these slopes a wide berth and avoid terrain features near cliffs where avalanches may be more likely. If you travel to elevations that did not see rain over the weekend, expect deeper snow and larger avalanches.

Avalanche problems

  • Wind Slabs

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

    As we roll into our next storm cycle, significant winds will help to drift old and new snow into dangerous Wind Slabs on Thursday. Wind 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. These slabs generally develop 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. In wind-sheltered locations or at lower elevations, you could be dealing with Dry Loose avalanches. 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.

    (1/31/2021) Example of a Wind Slab with textured snow surfaces that you can be on the lookout for on Thursday.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    3

    Beautiful weather on Wednesday allowed us to look around at many of the surrounding peaks and take stock of avalanches from the previous atmospheric river event. Crowns were easily found on multiple aspects, some of which were very deep and widely propagating. Most crowns were found near the base of cliffs or where terrain rolled over more steeply and connected terrain features. We do not have confirmation that any of these ran on the Mid-January crust/facet combo at this time, but some of them certainly looked deep and wide enough. Avalanches from this cycle were confirmed to have failed on the Mid-January crust/facet combo in the neighboring Stevens Pass and West South zones. As we roll into another loading event, we’ll further test this layer and see if another round of deep and destructive avalanches occurs. Continue to be leery of large open slopes and start zones, especially during periods of rapid loading through wind or precipitation.

    (2/24/2021) The atmospheric river event caused Chair Peak to avalanche naturally. It propagated widely with a crown depth estimated to be deeper than 2 meters in some locations. The debris made it all the way down to Source Lake. [SE ~5800'. Photo: Jeff Tarshis]

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 previous cycle produced some very large avalanches in the zone, both naturally and through control work by WSDOT’s avalanche crew. The atmospheric river event responsible for these avalanches left us with a crust (2/23), that becomes less pronounced and more deeply buried (as much as 45cm has been measured) as you ascend in elevation. The snow atop this crust has some weak graupel mixed in with it and could act as a potential weak layer the next few days. 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 ~5400’), 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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