Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Out of date — this forecast expired 5 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Big changes in the weather on top of a very deep and potentially weak snowpack will continue to maintain dangerous avalanche conditions. As the weather begins to clear, don’t let the draw of all the fresh snow overload your decision-making. Give the snowpack time to adjust by staying off of open slopes greater than 35 degrees.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    The Pass just received another 20+” of snow since Feb 25th. This fell with very strong winds and high precipitation rates. As a result, several potential weak layers exist on which you could trigger an avalanche. At mid and upper elevations, these slabs may present more like wind slabs with firm hollow surfaces that can break above you. Either way, with all the new snow and all the strong wind, give the snowpack time to adjust and stay off of open slopes greater than 35 degrees. As you travel you can observe the new snow and its layers by using simple hand pits, hand shears, and small slope tests. These observations work well on the softer storm slabs but could prove less useful on the firmer wind slabs. Take a close look at the base of the recent snow for a layer of graupel, surface hoar, and a thin crust which have all been observed at this interface and resulted in avalanches both Thursday and Friday. If an avalanche fails on these weak grains it may propagate widely or wrap around features.

    (2/25/2021) This small human triggered storm slab failed on a layer of graupel Thursday in the Alpental Valley. Similar observations were reported from other parts of the zone. NE, 4500' 6" deep. SS-ASc-D1-R2-I Photo: Ian Nicholson

  • Loose Wet

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

    A big change may await the snowpack on Saturday if the sun comes out. You could see natural loose avalanches that entrain significant amounts of snow and even grown large. These slides should stay isolated to very steep and rocky features, but don’t let them catch you off guard. If you start to notice the snow falling from rocks or trees, pay attention. This will serve as your first warning that the snow surface has become wet and unstable. The slopes and treetops above you could be basking in the sun even while you shiver in the shade. When you notice shedding snow or see new rollerballs, give steep slopes on similar aspects a wide berth. While loose slides can seem easy to predict and slow, if they catch you they can carry you into trees or gullies.

    (2/24/2020) Example: Rollerballs like these are a great indication that the snow surface is becoming wet and unstable. They can be the precursor to loose wet avalanches. When you see new rollerballs, steer away from similar slopes.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3

    Plenty of uncertainty continues to surround the deeper weak layers in the snowpack and that’s why they remain on our minds. It can be easy to write them off after this week’s atmospheric river. However, very large and destructive natural avalanches on Hwy 20 and Hwy 2 since the end of that loading event should have us questioning our assumptions. This layer is deep at the Pass; 8-10+ feet deep. It will take a very large trigger like a cornice or other slide to trigger an avalanche this large. Unfortunately, if a slide fails on these deep layers it would result in a very large and unsurvivable event. Let the potential consequences of this tricky avalanche problem shape where and how you travel. Consider limiting your exposure or staying out of large avalanche paths entirely.

    (2/24/2021) In Kendall Lakes, a slab ripped out at the base of the cliffs during the atmospheric river, spanning the entirety of the bowl [S-W, ~5200']

Avalanche Discussion

Saturday should be a nice day to enjoy the mountains. Don’t let the lull in the weather and the temptation of fresh snow shortcut your decisions. February has been an incredibly snowy month. Even this week, several feet of snow accumulated at Pass level. Big storms like this need time to gain strength. 

Several potential weak layers still exist in the snowpack. Three prominent layers are worth noting. 

  1. The 2/25 interface, mentioned above, may contain graupel, surface hoar, or a thin sun crust depending on aspect and location. You may find this layer at the base of the recent storm snow. 
  2. The firm atmospheric river crust (up to ~5400’) should sit just a few inches deeper. This can serve as a prominent marker to help identify events. 
  3. The mid-January facet-curst layer could remain intact 8-10 ft (230-300cm) below the surface. 

In addition to these potential weak layers, cornices grew very large and overhung during this stormy period. Give these giants a healthy amount of space. This includes staying out from under slopes where they loom above. 

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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