Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

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

On this New Years day you may be able to trigger avalanches in the recent snow both in wind-exposed and sheltered terrain. Watch for natural wet avalanches on steep, sunny slopes. Consider the possibility very large avalanches 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

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Expect the sun to warm steep, southerly slopes and to trigger loose avalanches. You may see these start near steep rocky terrain or near cliffs. As the day warms, you can avoid natural avalanches by sticking to more shaded, northerly aspects. If you see avalanches big enough to bury you or widespread activity on sunny slopes, consider that you're dealing with dangerous conditions. In this case you may want to avoid all steep, southerly terrain.

    On steep, shaded slopes, you can trigger small loose avalanches, especially on unsupported features. These avalanches will be less dangerous and easier to manage as we don't expect natural activity.

    Winds have been strong enough to transport snow at upper elevations. Look for recent drifts or cracks shooting through the snow as indicators that you can trigger wind slab avalanches on leeward slopes.

    (11/25/2022)

    An example of small loose avalanches above Highway 20 from earlier this seaon.

    Photo: Willie Webster

  • 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 challenging to predict and can break in surprising ways. You can dig and use snowpack tests to identify and confirm the presence of the weak layers. The last reported persistent slab avalanche was on Dec 27th. Human triggering is becoming more difficult. The uncertainty of this problem combined with warming temperatures and sun expected on Sunday is maintaining concern for an isolated, very large avalanche.

    Snow profiles suggests that recent natural avalanches 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, you'll find an overall shallow, weaker 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.

Here's a recap of 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. One very large (D3.5) debris pile was reported on the east end of Delancey Ridge. This avalanche could have involved weak layers near the bottom of the snowpack, though it hasn't been confirmed.  A crown, reported in the Vasiliki Ridge area on a northwest aspect around 7,400ft was deep enough that it may have also run in the lower snowpack . On Thursday, observer Willie Webster,  reported a couple of very large avalanches on westerly aspects in the Hairpin Valley. 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 same layer of surface hoar near the confluence of the Cutthroat and Early Winters dranaiges.

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 over 2 feet below the surface near Washington Pass and near the surface in the eastern foothills.

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