Avalanche forecast

Snoqualmie Pass

Northwest Avalanche Center
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Avalanche danger

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

Expect a rapid increase in recent snowfall above 4500 ft and with it, increasing avalanche danger. Storm snow layers are starting to heal, but you can still trigger them on an unsupported rollover, very steep slope, or where winds have drifted snow more deeply. Dial back your terrain selection further if you move into above treeline terrain where 3-4 feet of snow has fallen and significantly redistributed in the last 5 days.

Avalanche problems

  • Storm Slabs

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

    By Thursday, we're only 24 hours removed from a major storm. The Alpental upper station has received 42" of snow since 2/3. Avalanche danger increases sharply above 4500 ft where the snowpack becomes deeper temperatures kept the snow cold since the storm. The snow is wind effected on exposed aspects such as the SW slopes of Mt. Snoqualmie (photos in image gallery). Snoqualmie Pass received heavy snowfall Tuesday and Tuesday night so we still think you can trigger an avalanche if you push the terrain to the limit. Although inter-storm interfaces have not been notable, layering exists with some questions still remaining regarding the 2/3 crust interface keeping us off high-consequence terrain features.  Therefore, 3 ft or more of snow may be in play for avalanches. Avalanche would likely be large, deeply entraining, and difficult to manage.  Use the terrain to your advantage. You're most likely to trigger an avalanche on a steep rollover in the terrain, or on slopes steeper than 40 degrees. Wind loading will also increase your risk where Tuesday's slabs linger or if E winds start loading snow onto atypical (and more easterly) aspects. You can start to expand your terrain selection onto planar and well-supported slopes less than 40 degrees near treeline. As you approach upper elevation ridgelines avoid all slopes steeper than 35 degrees, giving the large amounts of recent snow more time to settle. If you find evidence of significant post-storm avalanche activity or hear whumphs in your terrain, dial back your terrain selection and reduce your exposure to consequential terrain.

     

    (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

We think that moderate E winds combined with cool air flowing from the east slopes of the Cascades will keep wet loose at bay even as the sun makes an appearance in the afternoon. If we're wrong, take the warning signs of moistening snow surfaces and rollerballs to avoid getting caught in a small avalanche on steep slopes facing the sun.

We remain with a two-tier snowpack structure. Above 4500 ft, the snowpack is deep and winterlike in near and above treeline terrain as described in the storm slab problem. Below treeline, fresh snow provides good riding conditions in open areas, but remains only 3-4" deep over a refreezing crust in the forest. 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.

 Although we do have some layers of concern below the 2/3 interface and above the MLK crust, we have not received word of any avalanches breaking down to these layers recently.

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