Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

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

Recent avalanches, additional snow, and strong winds point towards one thing, potentially dangerous avalanche conditions. Give the snowpack time to adjust and stay off of open slopes greater than 35 degrees. Destructive deep slides continue to plague the Cascades and should enter your discussion before you choose to travel in or near large avalanche paths.

Avalanche problems

  • Storm Slabs

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

    Several human triggered storm slabs were reported from Snoqualmie Pass on Saturday. At least some of them occurred in treed terrain and may have failed on the 2/25 interface. As we add more snow with warming temperatures to the snowpack, expect these conditions to continue. You may trigger avalanches on any open slope greater than 35 degrees including open treed areas. Slides failing down onto the 2/25 interface could occur on graupel, buried surface hoar, or a thin crust allowing them to trigger easily and propagate widely. As you ascend, the wind may drift snow into deeper slabs on some aspects allowing them to produce large and deadly avalanches.

    (2/27/2021) This skier triggered storm slab occurred on Saturday 2/27 in the Kendall Big Trees area. Other similar human triggered slides were also reported. N, 4500', 12-18" deep, 100' wide, SS-AS-D2-R2-U

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    It can be easy to downplay the potential for deep persistent slab avalanches. However, natural very large slides occurred near Stevens Pass and Crystal Mt within the last 24hrs. These destructive avalanches broke mature timber and ran to the valley bottoms. Let us be clear, this layer has not gone away and has only proven its ability to continue to produce avalanches. At Snoqualmie Pass, a suspected natural deep slab occurred on the flanks of Chair Peak during the most recent storm. While it may prove very difficult to trigger, a smaller avalanche or cornice fall could wake this sleeping beast. If you choose to enter large avalanche paths recognize the consequences you are assuming. Any avalanche on the mid-January layer would be devastating.

    (2/27/2021) This very large avalanche likely occurred during the storm sometime Friday 2/26. and may have failed on a deep persistent weak layer. SE 5800' Chair Peak area. Photo: Jeremy Allyn

Avalanche Discussion

Snoqualmie Pass could receive an additional 8” of snow by mid-morning Sunday. This will add to the 2-3 feet the zone accumulated since Feb 25th. The new snow should occur with a warming trend and may result in light rain at lower elevations before the precipitation ends. As a result, you could encounter loose wet avalanches at lower elevations Sunday. These slides should remain small and confined to very steep slopes near the rain-snow line. 

With all the recent storms, tracking the layers in the snowpack can grow tricky. While numerous potential layers and interfaces exist, three really stick out in our minds. 

  1. 2/25: At the base of the most recent storm snow you may find graupel, buried surface hoar, or a thin crust depending on aspect and location. This interface sat 12-18” below the snow surface on Saturday afternoon. 
  2. 2/23: A firm layer formed by last week’s atmospheric river may present as a stout crust up to ~5400’. While this layer has not produced avalanches, it can act as a marker and a means to interpret other storms. On Saturday, this layer was found roughly 3’ below the surface. 
  3. Mid-January: This facet-crust combination continues to stir conversation and fear. This layer is DEEP! And it will be extremely difficult to observe. You can probe for this firm prominent crust and may find it (if your probe is long enough) 9-10ft (275-325cm) below the surface. 

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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