Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Mon
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

An atmospheric river is primed to deliver rain, ice, and high-elevation snow to Snoqualmie Pass, creating very dangerous avalanche conditions in the process. The dynamic nature of this storm lends to a high degree of uncertainty surrounding timing. Your best bet will be to avoid traveling in or around avalanche terrain whenever it is raining. 

Avalanche problems

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2

    Below the rain/snow line, the atmospheric river will initiate a round of natural avalanches. These could occur within all three elevation bands, but middle elevations will be the sweet spot. That’s where significant dry snow currently exists, and rain is sure to fall during this next event. Look for avalanches to fail within the snow sitting atop the 12/6 interface or even down at this crust in isolated locations. You should avoid any slope where an avalanche can start, run, or stop if you suspect rain is falling on dry snow, even if that’s far above you.

    (12/6/2023)

    Example: A small wet slab that failed during our last atmospheric river event just across the zone boundary in the Salmon La Sac area.

    Photo: Katie Warren

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2

    Above the rain/snow line, we anticipate new snow to be heavy, creating an upside-down snowpack perfect for producing Storm Slab avalanches. You’ll need to dig down multiple feet to the 12/6 interface to look for heavy snow overlaying weaker snow, density changes, or snow failing in blocks during snowpack tests. Small test slopes or handpits may give you some indication of instabilities right near the surface, but won’t be enough to paint the full picture. If you see recent avalanches or determine that the snowpack is upside-down, avoid slopes over 35 degrees.

    (12/8/2023)

    Natural storm slab avalanches failed during a period of intense precipitation. 6-8 inches deep  SS-N-D1-R1-S

    Photo: Alpental Pro Patrol

Avalanche Discussion

There’s a lot of uncertainty around how this storm will unfold at Snoqualmie Pass over the next 24 hours. In an attempt to keep it simple, avalanche hazard should be highest in the morning hours before gradually decreasing throughout the day. Travel in avalanche terrain during this period is not recommended.

This atmospheric river is not expected to be as warm or as long as the one we experienced last weekend. We anticipate the majority of natural avalanche activity to be in the overnight and morning hours as rain soaks our currently dry snowpack. Of course, it's never that simple at the Pass. As an example, freezing rain is expected at some point and could alter the avalanche hazard depending on what elevation it falls at. Keep a keen eye on how the weather is unfolding and constantly rethink what avalanche problem is more likely and how that relates to avalanche potential. 

The depth of the 12/6 interface, which marks the end of our last atmospheric river event, varies depending on elevation. At mid to upper elevations, it could be as much as 3 feet deep by the time the brunt of this atmospheric river arrives. Regardless of its depth, the snowpack structure is the same. Wetted snow is below the 12/6, while dry snow sits above it. Multiple small avalanches were reported in recent days in the dry snow above the 12/6. We do not anticipate any avalanches failing below this interface on Sunday.

More rain will not help our already bleak travel conditions around Snoqualmie Pass. Swollen creeks will intensify while holes, rocks, and other natural hazards will continue to be of concern.

Regions covered