Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Thu
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Welcome back! Let’s shake the cobwebs off together on Wednesday as a dynamic storm potentially creates dangerous avalanche conditions. If you are in the mountains and notice signs of wind transported snow, use caution on slopes 35 degrees and steeper, convexities, and unsupported slopes where you could trigger avalanches more easily. Keep in mind that it is still early season and there are many natural hazards found on or just below the snow surface. 

Avalanche problems

  • Wind Slabs

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

    Wind slabs may be present on Wednesday on leeward slopes, at the base of cliffs, or on the sides of gullies at middle and upper elevations. These slabs should reach peak instability in the morning hours and may increase in size and reactivity as you ascend in elevation. Textured snow surfaces or pillow-like piles of snow are signs that can help to identify potential wind loaded areas for you to avoid. Hand-pits and small test slopes can give an indication of how the new snow is bonding to the old snow surface. If you find a poor bond or experience clues of unstable snow such as shooting cracks or whumpfing collapses as you travel, steer around wind-loaded terrain.

    Blowing snow, firm and textured snow, and cornice formation are all evidence that wind slabs are likely to be forming on lee slopes.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    With a mix of rain and snow forecast at lower elevations, it remains to be seen which form of precipitation actually falls from the sky, driving the avalanche danger. If most of the precipitation falls as snow, don’t be surprised to find some storm slabs at lower elevations on specific terrain features such as steep convex rollovers. Slabs could be deeper in areas where the wind was able to drift snow into piles, and you can use many of the same tests as with a wind slab to look for storm slab potential and poor bonding to the old snow surface.

    (11/23/2020) A quick skin track test as you travel can show you the upper snowpack's slab potential.

Avalanche Discussion

On Tuesday, NWAC team members observed two natural wind slab avalanches in the Snoqualmie Valley which were large enough to bury or kill you. Other observations from the zone continue to be limited, and the weather forecast is a tricky one for our zone, making this an avalanche forecast that is right on the line. What we do know is that we have a decent shot of precipitation coming Tuesday night, along with some moderate winds. When you have precipitation and wind together, that’s a good recipe for creating avalanches. If the storm continues to linger in our zone during the daytime hours or convergence sets up, snow may start to pile up and increase the size of potential slabs, and avalanches will be more likely. If we receive less precipitation than is forecast, you could see lower hazard, specifically at the lower elevations. Regardless of how the weather plays out, you should be prepared to make your own observations as you travel and choose appropriate terrain. When choosing terrain, be cautious, and consider the consequences of a fall. Falling or getting caught in an avalanche could result in a rough ride in the early season. Watch for shallowly buried rocks, stumps, crevasses, and creeks.

 

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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