Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Tuesday will be the final day of calm before the storm. Wind Slab avalanches will continue to be possible and may break in surprising ways.  As you ascend in elevation, be aware of wind-drifted piles of snow where you could trigger an avalanche more easily.  If you encounter firm, hollow-sounding snow, then head for lower angled slopes.

Avalanche problems

  • Wind Slabs

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

    We continue to receive reports of human triggered Wind Slabs in the Snoqualmie Valley zone. Earlier this week, strong winds created some unusual loading patterns, which has had us forecasting these Wind Slabs for a few days. We believe the largest and most unpredictable slabs to be on NE-N-NW aspects, but since we experienced a variety of wind directions, you should look for pockets of wind affected snow on all aspects. You are more likely to find these slabs as you ascend in elevation, with the possibility of them being large at higher elevations. You can look for smooth pillow-like piles of snow or textured surfaces to help you identify wind-loaded features. Use small test slopes to check the bonding and reactivity of these slabs. If you encounter firm, hollow-sounding snow, you could be dealing with more stubborn hard slabs that have been breaking in surprising ways throughout the region and you should head for lower angled slopes. Look out for convex rollovers, the sides of gullies, or the base of cliffs where windblown snow often accumulates and you could trigger an avalanche more easily.

    (12/28/2020) Skiers triggered two Wind Slab avalanches (D1) in the Crooked Couloir off Snoqualmie Mountain on Monday. In terrain like this, even small avalanches could be consequential.

Avalanche Discussion

The snowpack around Snoqualmie Pass contains an average of 20-35cm of snow over a prominent crust (12/21). Some areas have been stripped down to the crust by the wind, while other areas have wind drifted pockets as deep as 60-70cm. Below the 12/21 crust, the snowpack is generally strong and not of concern at this time. As was the case on Monday, any avalanche activity on Tuesday should occur above the crust, with avalanches possibly containing all of the recent snow. On Sunday, NWAC team members were able to confirm some weak snow grains above the 12/21 crust which could cause a point of failure. Alpental Pro Patrol recently had slabs release on these weak grains while large avalanches have been reported on this layer in the neighboring West South zone and elsewhere in the region. These slides have been breaking in some surprising ways and are generally found on NE-N-NW aspects which have been wind-loaded. In other zones, slabs with a similar setup have been failing after multiple people have successfully traveled over them, or have been remotely triggered, making predicting how and when they will break difficult. On Monday, multiple skiers in the Snoqualmie Valley triggered Wind Slabs skiing in steep rocky terrain or on convex rollovers. These slabs were on the smaller side in comparison to the hard slabs mentioned previously but show that the snowpack still has not fully healed from the last wind event. With a significant storm set to impact the area on Wednesday, look for an increase in hazard and further stress to be applied to our current snowpack setup.

The 12/21 crust is very firm and travel conditions can be difficult because of it. Allow yourself extra time and look out for open creeks and other early season conditions at lower elevations.

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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