Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Sat
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

You can trigger small avalanches at upper elevations where the wind drifted recent snow. A large trigger like a cornice fall in the wrong spot could trigger a large and destructive avalanche on deeper weak layers. Identify steep and unsupported terrain to steer clear of,  and give yourself a wide buffer away from complex terrain for the time being. 

Avalanche problems

  • Wind Slabs

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

    Look for freshly deposited drifts, stiffer snow, and cracks shooting from your feet or machine to indicate where you can trigger an avalanche. Windward, loaded slopes steeper than 35 degrees will be the most dangerous. Stick to lower-angle or wind-sheltered terrain. Use extra caution near cornices while traveling on ridges and make sure to give them plenty of space. There have been multiple reports of recent cornice falls, including some that triggered deep avalanches. Consider that triggering a smaller wind slab avalanche could be enough to gouge into deeper layers, resulting in a very dangerous slide. With more light snow accumulations in the forecast, you may be able to trigger small "sluffs," or loose avalanches,  in steep, sheltered terrain.

    (11/21/2023)

    An example of wind drifting snow near ridgelines.

    Photo: Matt Primomo

  • Persistent Slabs

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

    Minimize your exposure to overhead cornices. While these avalanches are difficult for humans to trigger, a cornice fall could provide enough force. Choose well-supported and lower-angle terrain. Stop and regroup in safer areas, with a wide buffer away from potential runout zones of overhead slopes. The snowpack further east in the zone is more shallow, so it would be worth using more caution near and east of Mazama. 

    There are two problematic weak layers; small facets buried on January 8th in the top 1/2 of the snowpack, and a series of crusts and large weak grains from December in the lower 1/3rd of the snowpack. These layers were reactivated by an intense storm on January 17th. Observations of large rumbling collapses have slowed. We continue to get reports of unstable snowpack test results, and since a warm-up on the 20th, we've received two reports of recent cornice-triggered avalanches on deeper layers. Although the chances of triggering one of these avalanches have declined, if you did trigger one, it could be 2 to 3ft deep and destructive.

    (1/25/2024)

    A recent natural avalanche (D1.5) may have run on an older weak layer and may have been initiated by cornice fall. Poster/Pika Pk NE, 7,2000ft

    Photo: North Cascades Mountain Guides

Avalanche Discussion

On Thursday, observers reported cracking in fresh wind slabs and enough wind transport to fill in tracks throughout the day. A recent natural avalanche was reported from the Hairpin Valley on Poster/Pika Peak, NE, 7,200ft. Observers believe the avalanche may have been initiated by a cornice fall and ran on a weak layer in the top 1/3 of the snowpack (50cm below the surface with HS 150cm). On the 24th, NWAC forecasters found 3 inches of new snow near Blue Lake. At a profile site (NW, 6,650ft), they found propagating test results on the January 8th facets ↓65cm and sudden collapse failures on old facets and crusts from December. The structure of older, stiff slabs over the thin, weak layer of January 8th facets, ~2 feet below the surface, matches a profile near the Poster Peak avalanche. On the 23rd, observers reported a number of small, loose, and wet avalanches of very steep, craggy terrain. Warming temperatures noistened snow surfaces up to about 6,000ft on all aspects. 

Another observation pertinent to persistent slabs is another large cornice-triggered avalanche in Cutthroat drainage that ran on a deeper weak layer and likely occurred on the 21st. Other deeper crowns have also been spotted since the January 16th storm, though visibility was poor. On the 21st, an observer in the Twisp River area found that the mid-December crust produced unstable propagation saw test results. They also experienced loud whumphs that shook trees as the collapse propagated widely across the terrain. The snowpack near Mt Tiffany near Conconully was found to be very thin, and the deepest area was only 2.5ft deep at 6,800ft. 

If you're in the mountains, please let us know what you find.

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