Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

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

New snow and wind will bring an increase in avalanche danger through Sunday and into Monday. You could trigger very large avalanches on buried weak layers, especially at middle and upper elevations. You may be able to trigger small avalanches due to fresh drifting in similar terrain.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–2.5

    New snow and wind may make triggering these dangerous avalanches easier on wind-loaded upper-elevation slopes. Put a larger buffer of terrain between your group and large start zones or complex avalanche paths above 6,500ft. Use extra caution where you find less than 5 feet of snow on the ground above 6,000ft. Choose smaller, supported slopes and stay well out from under larger features. Signs of instability can be inconsistent, creating a tricky problem that is essentially 'unmanageable.' You might not receive signs of instability before the whole slope fails. Facets that were buried throughout February can be found over a crust in the top 2-4 feet of the snowpack. There's copious evidence of these layers being the culprits of numerous very large natural avalanches and close calls in the zone. 

    (3/5/2024)

    A very large avalanche was remotely triggered by skiers on 3/2 on Kangaroo Ridge. The crown was ~70-100cm deep, and it ran on a layer of facets (1.0mm) buried in mid-February, just above the 1/31 crust.

    Kangaroo Ridge, Pk 8183, WNW, 7,600ft

    Photo: John Stimberis

  • Wind Slabs

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

    Southerly gusts will be strong enough to form new wind slabs, especially at upper elevations. Freshly drifted slabs may be easy to trigger where they formed over facets. Look for signs of wind slabs, such as blowing snow or thicker pillows of new snow, or cracks shooting through the snow. While you may be able to steer around these smaller drifts, you'll need to avoid triggering the much more dangerous persistent slab avalanches. You can trigger both of these types of avalanches in similar terrain.

    (1/23/2024)

    An example of plumes of blowing snow over a ridge of Hinkhouse Peak in January. Photo: Josh Hirshberg

Avalanche Discussion

NWAC is devastated to report the death of one of our Avalanche Forecasters, Matt Primomo. Tragically, Matt passed away in a non-avalanche accident away from work on Thursday, March 7th. Matt has been a key member of the NWAC family since 2017. His life in the mountains touched so many people. We are absolutely heartbroken. Please join us as we mourn this immense loss with Matt’s family, friends, and community.

 

Discussion:

A weak storm is forming the next set of layers on the snowpack. This snow is likely burying a range of crusts, facets, and possibly surface hoar.  Observers reported crusts and loose (wet and dry) avalanches on steep, sun-exposed slopes this week. In the past week, avalanches and signs of instability on persistent weak layers have slowed.

On the 5th, forecasters visited the site of a remotely triggered (D3) avalanche on Kangaroo Ridge. They found that the avalanche was ~2.5-3 feet deep and ran on a layer of facets buried in mid-February, just above the Jan 31st crust. Tests still produced sudden or propagating results indicating that backcountry travelers could trigger similar avalanches, especially in areas of relatively shallow snowpack. There have been multiple reports of close calls, natural avalanches, and snowpack observations in the Highway 20 corridor that point to the deep, persistent slab problem. Widespread, very large natural avalanches occurred between February 28th and March 3rd. In the past week, natural avalanche activity has stopped, and snowpack tests have become more variable, with some showing relatively stable results. In the East Central and Stevens Pass zones, there have been multiple triggered avalanches and involvements this week on a similar snowpack structure.

Snowpack information is limited outside of the Highway 20 corridor and Harts Pass. Let us know what you find if you get out into the backcountry!

Regions covered