Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

Tue
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

A heftier shot of precipitation accompanied by increasing winds should be enough to get us to dangerous avalanche conditions by the end of the day on Monday. As you ascend in elevation, look for wind-drifted piles on specific terrain features in the morning hours. Once 6” of new snow has fallen, be on the lookout for more widespread avalanche activity and start to question slopes over 35 degrees.

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–1.5

    Sunday night and Monday should be the largest shot of precipitation the Pass has seen since this storm parade started on Friday morning. An increase in wind speed and cooling temperatures should accompany the precipitation, possibly resulting in Wind Slabs for you to manage Monday morning. These slabs will be more likely as you ascend in elevation above this weekend’s rain/snow line. Look for them on the leeward side of ridgelines, convex slopes, or near rocky terrain such as cliffs and gullies. Use visual clues such as actively blowing snow, newly developed cornices, or textured surfaces to help identify wind-loaded slopes to steer around.

    As the day progresses, the snow should start to pile up and the distribution and likelihood of triggering slabs may expand. Once we cross the threshold of 6” of new snow, start to think about Storm Slabs on a larger variety of slopes. Using quick hand pits as you travel to check the depth of the new snow and how it has bonded is a great way to keep tabs on how the storm is unfolding. Small test slopes or uptrack tests can give you an indication of how the new snow is reacting to your weight. If you notice it failing in blocks or determine that there is a poor bond, you should avoid slopes over 35 degrees. 

    (2/5/2023)

    Shallow Storm Slabs were triggered by avalanche professionals on Cave Ridge on Sunday. These ran on a firmer crust. [SE 5500']

    Photo: Jeff Tarshis

Avalanche Discussion

It’s been a wet weekend at Snoqualmie Pass, with several pulses of precipitation impacting the zone since Friday. As of Sunday night, just under 1 inch of water has fallen, resulting in roughly 4-8 inches of new snow. Fluctuating freezing levels during this timeframe have essentially created two different elevation bands you should be aware of. 

At lower elevations, wet and gloppy snow was found throughout the zone and wet avalanches were reported by multiple parties and professionals. On Monday, we anticipate that hazard will be minimal at these elevations despite the incoming storm. That said, another bump in freezing levels or snow falling and drifting into deeper piles over on a firmer crust could create some problems, particularly at the upper end of the below treeline band. 

As you ascend in elevation, you’ll reach a transition point where the snow becomes much drier. This elevation was found to be around 4200’ on the eastern end of the zone by NWAC forecasters on Sunday. This is where you will start to encounter a more layered upper snowpack and likely more avalanche potential. You should investigate all of the snow that has fallen since Friday (2/3 interface) for weaknesses as we continue to add load. In isolated locations, there could be weak snow lingering at this interface. You're more likely to find a crust that could make a good bed surface for avalanches to run on. On Sunday, various avalanche professionals identified midstorm instabilities and even triggered very shallow Storm Slab avalanches on steeper slopes. 

While not a huge storm, this is the largest punch we’ve had in recent days. With snow forecast to fall all day and into the evening, combined with this weekend’s accumulations, we should have enough to reach dangerous avalanche conditions by day’s end. An even larger pulse arrives on Monday night into Tuesday and will likely result in more widespread avalanche activity. We may start thinking about some of those deeper layers between the 2/3 and MLK crust if this turns into a whopper.

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