Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

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

A warming upper snowpack creates overlapping avalanche problems, making it very difficult to travel safely in complex terrain. Avoid all open slopes steeper 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

    Warming temperatures are creating a dense and dangerous slab near the snow surface that you can trigger throughout the terrain. Several human triggered storm slabs were reported from Snoqualmie Pass over the weekend. 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 multiple graupel layers, 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

    Deep persistent slab avalanches continue to dictate the terrain selection of avalanche professionals in the Snoqualmie Pass region. Natural very large slides occurred near Stevens Pass and Crystal Mt within the last 48hrs. These destructive avalanches broke mature timber and ran to the valley bottoms.  At Snoqualmie Pass, several natural deep slabs occurred on the wind-loaded E flanks of Chair Peak during the most recent storm.   The mid-January crust-facet layer has endured several loading events and continues to produce destrictive avalanches. A large and overhanging cornices triggered a size 2.5 avalanche off Bryant Peak on Saturday. More cornices may fail as temperatures warm on Monday. While the weight of humans are less likely to directly trigger this problem, smaller storm slabs, wind slabs, or cornice failures drastically increase the likelihood of disturbing the deep one. 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

  • Loose Wet

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

    There's plenty of cold, low-density snow that will weaken quickly and move downslope with warm temperatures and any sunshine that makes it through the clouds on Monday. Many slopes will start the day with a thin crust and refrozen rollerballs on most steep slopes from Monday. Daytime warming or sunshine will break down the thin crust and, opening the door to another round of rollerballs and wet loose avalanches. Several wet loose natural avalanches were reported and grew to size 1.5. It is difficult to predict how deeply slides will entrain on Monday, but any signs of larger avalanches should be a serious red flag. As the snow surface melts, choose colder, shaded aspects and slopes less than 35 degrees without exposure to slopes receiving sunshine. Keep in mind that this problem may be slow to materialize if cooler E flow in the morning prevents warming until the afternoon. 

    (2/28/2021) Rollerballs and Wet Loose activity.

Avalanche Discussion

Warming temperatures will add uncertainty to an already complex snowpack that has seen a massive depth increase in the last 5 days. Snoqualmie Pass has picked up 42" of snow since Feb 25th with the last several inches arriving on a warming trend that ended with rain at pass level.

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 and may become shallower as the snowpack consolidates. 
  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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