Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

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

Another round of snow and wind will bring increasing avalanche danger. Small avalanches in freshly wind-drifted snow will be the most likely problem to encounter. But more dangerous is the potential to trigger very large avalanches on buried weak layers, especially at middle and upper elevations. Avoid steep wind-affected terrain at mid and upper elevations. 

Avalanche problems

  • Persistent Slabs

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

    The incremental loading with continued small amounts of new snow and wind will make it easier to trigger these dangerous avalanches. Put a larger buffer of terrain between your group and large start zones or complex avalanche paths above 6,500ft. Use extra caution in areas 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 buried throughout February exist 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

    Steady, moderate winds and fresh snow will form new wind slabs. Freshly drifted slabs may be easy to trigger where they form over facets. Look for signs of wind slabs, such as blowing snow, thicker pillows of new snow, or cracks shooting through the snow. Slopes below corniced ridges, the base of cliffs, and confined terrain features are likely spots for wind slabs to form. 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 will be closed on Tuesday, March 12th, as we gather and grieve following the death of one of our forecasters, Matt Primomo. We will not issue regular avalanche or mountain weather forecasts on Tuesday. We will return to normal operations on Wednesday, March 13th. We appreciate the community's understanding and support during this time.

Discussion:The incoming snow will fall on variable surfaces of crusts, facets, and possibly surface hoar and may form a poor bond with the new snow. Quick hand pits and test slopes can offer a great way to observe this new/old snow interface. But these tests won't give you insight into the deeper, more consequential persistent slab problem. 

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