Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
2 · Moderate
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Out of date — this forecast expired 6 years ago.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

Warmer temperatures and continued precipitation could be enough to tip the scales and produce avalanches on Sunday. Keep an eye out for wind-drifted piles of snow to steer around or red flag signs of instability such as shooting cracks and whumpfing collapses. If you notice these signs or witness rain falling on dry snow, head for lower angled terrain.

Avalanche problems

  • Wind Slabs

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

    Another day with a few inches of snow and some light to moderate winds may build fresh Wind Slabs or thicken existing slabs at Snoqualmie Pass. Look for Wind Slabs to be more reactive near rocky features such as gullies and cliffs, or on leeward slopes near ridgelines. Some of these slabs may be sitting on buried weak snow grains, causing them to break in surprising ways, meaning you may need to manage them a little differently than what you may be used to up at the Pass. Take some time and dig down to the 1/13 crust to look for the existence of weak snow or poorly bonded interstorm layers before committing to terrain. Use test slopes to check the reactivity of all of the snow sitting atop the crust to see how it reacts to your weight. Feel for subtle changes in the snow as you travel, look for textured surfaces or smooth pillow-like piles of snow to key you into the terrain features you should avoid. 

    (1/30/2021) This shallow slab was triggered by skiers who were skinning across this convexity on Saturday (1/30). The slab propagated the width of the feature.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Rising freezing levels should be kept mostly at bay on Sunday by the east flow at the pass proper, but we wouldn’t be surprised if some rain mixes into middle and lower elevations by the end of the forecast period. Areas of the zone not as heavily influenced by the east flow may have a higher chance of seeing rain. If you experience rain falling on dry snow, expect to see some small Wet Loose avalanches on steep slopes. Look for these slides to start at a point, such as where snow sheds off trees and rocks, and then fan out as they move downhill. They are capable of entraining lots of snow and even triggering slabs as they descend. If initiated on Sunday, they may gauge down and involve all of the snow above the 1/13 crust. Head for low angle terrain away from steep slopes above you if it starts raining on dry snow.

    (12/19/2020) Example of a small (D1) Wet Loose avalanches that could occur if rain falls on dry snow on Sunday.

Avalanche Discussion

Weak snow grains in the form of buried near-surface facets and possibly buried surface hoar are at the top of our concern list as snow depth above the 1/13 AR crust continues to increase. We have not had a lot of confirmed activity on these weak layers as of yet, but neighboring zones have seen plenty of avalanches on a similar snowpack setup. Areas that contain a slab are triggering easily, propagating widely, and running downhill quickly. At Snoqualmie Pass, we received observations of a few small avalanches that appeared to have broken on facets on Saturday. We believe that wind loaded areas have the highest likelihood of triggering a slab on these persistent grains. 

Although there is not a lot of new snow expected on Sunday, temperatures should be warmer than recently. Any new snow could potentially create an upside-down warm heavy snow over dry light snow scenario. If these slabs develop with more snow or wind than expected, we could come closer to our tipping point for widespread avalanches. In this scenario, you should be on the lookout for red flag signs of instability such as whumpfing collapses and shooting cracks in the snow as an indicator that avalanche hazard has increased. These weak grains may not be everywhere, but if you happen to trigger an avalanche on them, it could break in surprising ways. Areas in the eastern part of the zone could be even more likely to produce these surprising avalanches. Help us out by letting us know if you see (or don’t see) avalanches, cracking, whumpfing, or weak snow on Sunday by submitting a public observation. 

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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