Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

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

The Pass has received almost constant precipitation since Friday, resulting in dangerous avalanche conditions. You could run into a number of new snow problems out in the mountains on Wednesday as you ascend in elevation. Your best move will be to avoid slopes over 35 degrees as the snowpack adjusts to the recent load.

Avalanche problems

  • Storm Slabs

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

    The storm isn’t quite over yet. We should still squeeze out a few more inches of snow before skies start to clear on Wednesday. Slabs will be larger, and possibly more reactive, as you ascend in elevation above the rain/snow line (~4500'). Take the time to investigate all of the recent snow above the 2/3 interface for storm instabilities, a poor bond, or heavy over weak snow. You should dig with your shovel or hand to look for these potential points of failure. Visual clues such as recent avalanches, shooting cracks, or whumpfing collapses as you travel are bullseye information that the snowpack needs more time to heal. You can also use small test slopes to see how the storm snow is failing under your weight. If you notice it is failing in blocks or see any of the signs of instability listed above, avoid slopes over 35 degrees.

    Reports from Tuesday indicate there was plenty of wind transport of the newly fallen snow as well. The management of Wind Slabs is not much different in this case than that of the Storm Slabs. You should avoid slopes over 35 degrees if you suspect them to be wind-loaded. Be cautious on the leeward side of ridgelines or anywhere you notice smooth pillow-like piles of snow.

    (2/7/2023)

    Alpental Pro Patrol triggered widespread large avalanches during their mitigation efforts on 2/7. Most crowns were between 1 and 2 feet deep.

    Photo: Alpental Pro Patrol

  • Loose Wet

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

    In addition to the larger and more dangerous slabs, there are other new snow issues you might encounter on Wednesday above the rain/snow line. The sun is forecasted to make an appearance in the afternoon and could destabilize the snow surface resulting in Wet Loose avalanches. This may not pan out, but if the conditions are met these avalanches could grow large and are worth putting on your radar. Look for snow shedding from trees and rocks or fresh rollerballs/pinwheels on sun-exposed slopes. These are precursors to Wet Loose avalanches and should be a sign for you to head for shadier slopes. These slides often start at a point and then fan out as they descend, possibly growing large or even triggering slabs. On some slopes, this same process could manifest as solar-induced Dry Loose. Their activity, signs, and management are the same. If you suspect that a loose cycle is imminent, head for shadier slopes away from overhead hazard. 

    The kicker on this one is that you could also see some wet avalanches at lower elevations where rain fell during this event. Same problem, but a different set of circumstances. We believe this activity should be muted due to the cooling trend and several rounds of liquid precipitation impacting the area since Friday. That said, if you find that the snow is moist and punchy or see those same signs such as rollerballs and pinwheels, you could encounter some Wet Loose avalanches on slopes over 35 degrees.

    (1/20/2023)

    Example: A natural avalanche that may have started as a loose coming off the sun-exposed upper slopes or from a small cornice fall. It triggered a small slab as it descended, leaving behind a crown just below the confined gully. [E 6000']

    Photo: Andy Harrington

Avalanche Discussion

It was a stormy day at Snoqualmie Pass on Tuesday with heavy snowfall at upper elevations and more liquid precipitation down lower. This has created a two-tier elevation band with drastically different conditions as you ascend above roughly 4500 feet. Observations from the day are limited due to the ferocity of the storm, but Alpental Pro Patrol reported widespread large slab avalanches triggered during control work. Most of these slabs were around 1 foot deep, with some as deep as 2 feet in wind-loaded areas. They also noted some natural avalanches with 1 foot crowns on steep, unsupported slopes. Multiple avalanche professionals above the rain/snow line in the Kendall area reported Storm Slabs with failing midstorm density breaks, shooting cracks, and plenty of actively blowing snow forming new Wind Slabs. Visibility was poor, but a few natural avalanches were spotted on steeper slopes. All parties mentioned wet avalanches being a concern at lower elevations with at least a few naturals running during the day.

On Wednesday, we should start to make our way out of this storm and although peak instability may have been passed for natural activity, slopes are now primed for human triggers. We continue to believe that the roughly 2-2.5 feet of snow that has fallen since Friday (2/3 interface) is in play for avalanches. This is the area where you should focus your observations. Although we do have some layers of concern below this interface and above the MLK crust, we have not received word of any avalanches breaking down to these layers as of Tuesday evening.

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