Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

On Saturday, you may be able to trigger avalanches in the new snow as temperatures warm. Consider the possibility of triggering a very large avalanche on deeply buried weak layers. Expose only one person at a time to avalanche terrain and make sure to stop and regroup well-out from under large pieces of terrain. 

Avalanche problems

  • Storm Slabs

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

    You may be able to trigger avalanches in the surface snow. Use small test slopes and quick tests to check how the new snow slides. If you see cracks in the snow or test slopes that slide easily, steer around typical trigger points and steep slopes. This includes unsupported slopes, convexed rolls, and rocky slopes over 35 degrees.  With ongoing snow and warming temperatures, the storm snow may stick together as a cohesive slab. Look for heavier, stiffer new snow over softer layers as an indicator of this problem.

    If the new snow is less cohesive, you may be able to trigger loose avalanches in steep terrain.  If the sun comes out, you may see some small wet avalanches on steep, sunny slopes.

    (12/30/2022)

    An example of a small storm slab avalanche form Friday on Stevens Pass. If the new snow is cohesive, you may be able to trigger similar avalches.

    Photo: NWAC public obs

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    These avalanches may be difficult to trigger, but the consequences could be serious. Persistent slab avalanches are difficult to predict and can break in surprising ways. You may be able to trigger them where the weak layers are most developed. You can dig and use snowpack tests to identify and confirm the presence of these layers. The last reported natural persistent slab avalanche was on Dec 27th. 

    Snow profiles suggests that natural avalanches at the beginning of the week involved the Dec 8th buried surface hoar layer (3ft below the surface) with at least one suspected to have run on sugar-like facets from November deeper in the snowpack. If you're traveling well to the east of the Cascade crest, near the Silverstar drainage, or near and east of Mazama, consider that avalanches could potentially involve most of the season's snowpack.

    (12/28/2022)

    A very large avalanche (D2.5) that occurred during the Christmas Storm. Potentially ran on weak, faceted grains from November. Vasiliki Ridge, NW, 7,400ft

    Photo: Jeremy Allen

Avalanche Discussion

On Friday, observers on Delancey Ridge experienced a large collapse at 6,500ft on south aspect. They believe it may have been due to a deeper weak layer, possibly older facets from early season. Other observers reported that the new snow was light and right-side up, showing few signs of instability.

We have good evidence that a cycle of very large, natural avalanches occured around the 24th and continued to as recent as the 27th or 28th. Observers reported at least 4 very large, size D2.5-3.5, natural, slab avalanches that ran roughly between December 24th and 27th. At least one very large avalanche may have involved weak layers near the bottom of the snowpack, though we haven't been able to confirm this.  A deep crown was reported in the Vasiliki Ridge area on a northwest aspect around 7,400ft. On Thursday, observer Willie Webster,  reported a couple of these very large avalanches on westerly aspects along with smaller avalanches in storm snow in the Hairpin Valley vecinity. Willie's snow profile nearby found the problem layer to likely be a layer of surface hoar, believed to be buried 12/8, over 3 feet below the surface. On Tuesday, I found similar, propagating test results on the 12/8 surface hoar near the confluence of the Cutthroat and Early Winters dranaiges. On Wednesday, a long-time avalanche professional reported occasional collapses in the mountains just north of Mazama. See photos and video below. 

Heavy snow and rain brought over 3.5 " of water equivilent to the Washington Pass weather station on December 23-27th. A thick crust was buried on the 25th and the load activated weak layers that have been lurking for many weeks. The crust is now 2 feet below the surface near Washington Pass and near the surface in the eastern foothills.

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