Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

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

Stormy weather will cause the avalanche danger to spike Thursday morning. Heavy snowfall rates and strong winds could even result in a few natural avalanches. Pay attention to the slopes above you and stick to generally lower angled or treed terrain to avoid the potential avalanches.

Avalanche problems

  • Storm Slabs

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

    Snoqualmie Pass could receive a foot or more of snow over just a few hours Thursday morning. Snowfall rates like this often result in slab avalanches. Expect very steep and rocky slopes to quickly shed the new snow load and produce a few small natural avalanches. As more snow accumulates, that’s when things become dangerous. You could trigger soft slabs on open slopes greater than 35 degrees particularly during or immediately after periods of stormy weather. At mid and upper elevations, moderate to strong winds could help some of these slabs to grow larger and easier to trigger. While the snow may feel very soft, this could be a touchy day. 

    One large portion of uncertainty for Thursday’s storm slab forecast is what will the new snow fall on? Very cold weather the last few days may have allowed the snow surface to become weak and facet. You can look at the base of the new snow for sugar facets, feathery surface hoar, or just blocks that fail and slide easily in uptrack and hand pit tests. If you suspect weak snow, dial it back. Even slopes that are only 30 degrees or in large open timber should be suspect.

    (12/22/2021)

    You can dig with your hand to look at the new storm snow and search for buried weak snow.

    Photo: Andy Harrington

Avalanche Discussion

Brrr! Its’ been cold at the Pass this week! We expect more chilly weather tomorrow. You could even encounter wind chill values well below 0F. 

Snoqualmie Pass received 4-5 ft (120-150cm) of snow over the past week. This storm snow has settled nicely. Many reports from across the zone indicate a generally right-side-up snowpack that is well bonded to the Solstice Crust. While you may find layers in the recent storm snow, avalanche concerns should remain largely at or above the new/old interface. One exception, a thin weak sun crust formed on steep SE-SW aspects on 12/27 and currently sits just a few inches below the surface. This is another spot to look for weak snow. Given the stormy weather and potential for weak snow, this could be a good day to ease into terrain and use small low consequence slopes to gather information.

Very large avalanches in wind-loaded snow were reported on Chair Peak (Snoqualmie Pass), Mt Mastif (Stevens Pass), and Shuksan Arm (West North) December 26-27. These slides highlight the potential for larger, much deeper avalanches, especially in rocky and complex terrain at upper elevations. While these slides would be hard to trigger, they would be catastrophic. As we add more load to the snowpack Thursday, the uncertainty around the potential for similar avalanches remains. Make sure to talk about this looming piece of uncertainty before stepping into big, high-consequence slopes. 

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