Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 3 years ago.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

Highlights

A second and more powerful atmospheric river is headed for Snoqualmie Pass. Very dangerous avalanche conditions will exist whenever the switch to rain occurs. That would be a marvelous time to exit avalanche terrain and wait out the rest of this storm somewhere dry.

Avalanche problems

  • Storm Slabs

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

    Sunday night should be a brief break between atmospheric rivers, allowing freezing levels to drop and a surface crust to form. As a new wave of precipitation arrives on Monday morning, it could take some time to warm up. You’ll be dealing with new snow problems until it does. Look for cracking of the surface, whumpfing collapses, or a poor bond to an underlying stiff crust as indications that avalanches are possible on slopes over 35 degrees. These avalanches should primarily be small unless the warm-up is heavily delayed, allowing for more snowfall. 

    (12/2/2023)

    Cracking and failing blocks of snow during tests at lower elevations indicate an unhappy snowpack.

    Photo: Ian Nicholson

  • Wet Slabs

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

    Once precipitation switches to rain, you’ll be dealing with more significant hazard. Expect natural avalanches to occur on slopes over 35 degrees. You may initially notice loose avalanches as this change occurs. More dangerous slab avalanches could fail once Sunday night’s crust is broken down. These slides could travel long distances in open terrain and entrain much of this season’s snowpack. On smooth rock ledges or grassy slopes, the entire snowpack could fail. Traveling in avalanche terrain is not recommended once the rain has begun.

    (1/13/2023)

    Example: Wet avalanches near ridgeline from an atmospheric river last season.

    Photo: Trevor Kostanich

Avalanche Discussion

Monday’s weather makes the Pass renowned but challenging from a forecasting perspective. Multiple competing meteorological factors will be in play, resulting in many if/then scenarios playing out in the snowpack. The general consensus is that the incoming atmospheric river and warm temperatures will eventually win the battle, and freezing levels will sore to 7500’. This will result in rain at the tops of all the mountains in our zone.

The timing is where our uncertainty lies. We believe this transition will happen in the midday hours, and that’s how we have shaped our forecast. However, if it occurs earlier, you’ll be dealing with more dangerous wet problems all day. If it happens later or not till the overnight hours, you will be dealing with dry snow problems and the anxiety of when the switch may occur.

On Sunday, the switch to rain was delayed much longer than expected at mid to upper elevations. Additionally, the Pass did not receive as much rain as anticipated. Throughout Monday and Tuesday, we are confident that significant rain will occur on all aspects and elevations within our zone, kicking off a round of natural avalanches large enough to bury or kill you. 

Before the parade of atmospheric rivers, over 2 feet of snow fell from Thursday through Sunday morning, creating the 11/30 interface. The storm snow sits predominately on a melt-freeze crust at middle to upper elevations, while it rests on bare ground at lower elevations. This weak snowpack structure resulted in remotely triggered avalanches, shooting cracks, and whumpfing collapses on Saturday. Don’t ignore red flag signs of instability such as these as you travel. Even small avalanches could be consequential this time of year due to early-season conditions and hazards such as exposed rocks, open creeks, holes, or bushes.

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