Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Very warm temperatures, strong sun, and a poor overnight freeze will drive dangerous wet avalanches on slopes steeper than 35 degrees. Time your travel to be off of and out from under sun-exposed slopes before the snow becomes wet and weak. Avoid traveling on or under slopes with cornices and crevasse-like cracks.

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    Expect that there may be a poor overnight freeze and that snow surfaces may quickly become wet and weak.  If you sink into wet snow up to the top of your boots, you may be able to trigger an avalanche. Move off of steep slopes before the snow is unsupportive and weak. Look for melt-water moving into previously dry layers below the surface as an indicator of increasing danger.  Start your travel early. Plan ahead and give yourself options for travel that include a variety of aspects and elevations. Be ready to end your day early if conditions become dangerous.

    Wet avalanches will first be active on the east aspects and later on the west aspects. They will be bigger near and below treeline. Take note of how much surface snow has frozen or melted on various slopes.  You may find that conditions change dramatically from one slope to the next and from morning to afternoon.

    (4/11/2021) Natural wet avalanches ran in very steep, east-facing terrain. Stevens Pass zone

  • Glide Cracks

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2

    Glide avalanches are difficult to predict and can be very dangerous. They typically release during prolonged warm temperatures and can involve the entire snowpack. You can find crevasse-like cracks in the snow on steep, rocky slopes. These glide cracks are an indicator of where an avalanche could occur. Similarly, cornices loom over some ridgelines and may fall during the warm temperatures this week. Use extra caution to avoid being on or under slopes with glide cracks and cornices.

    On Wednesday, an observer reported a large glide avalanche on a known indicator path on the southeast face of Lichtenberg Mountain. There are many more glide cracks and snow-covered rock slabs than is typical for this time of year. We expect that other glide avalanches may occur in the coming days. The mid-January layer is about 6-8 feet below the surface and has yet to see melt-water on most slopes. This layer could produce very large avalanches as warming temperatures continue.

    (4/14/2021) A large glide avalanche occurred on the 14th. The bare rock slab bed surface is visible in the top, right corner. Lichtenberg Mtn, SE, 5,200ft. Photo: WSDOT

Avalanche Discussion

On Sunday through Wednesday, observers reported numerous wet loose avalanches on sun-exposed slopes with some on northwest and northeast aspects. A few of these were big enough to bury or kill a person. Both west and east winds transported snow earlier this week. Observers in neighboring zones have found weak facets on high elevation northerly aspects under recently formed slabs.

On Tuesday in upper Nason Creek, I found that surface conditions varied significantly by aspect and elevation. All but the most shaded slopes above 5,000ft were capped with crusts. The top two feet of the snowpack varied from mostly dry recent snow to all melt forms (from very hard to soft and weak) and everything in between. On Saturday, northerly aspects in the Lanham Creek drainage held mostly dry, winter-like layers with a handful of thin crusts in the top 5 feet of the snowpack.

A total of 1.5-3 feet of snow fell in two different storms on the 7th and 9th.  Many northerly slopes still hold a mostly dry snowpack. On east through south through west aspects, the upper snowpack consists of mostly melt forms in various states of being melted or frozen. 

Daily avalanche forecasts will end on Sunday, April 18th.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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