Avalanche forecast

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Northwest Avalanche Center
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Avalanche danger

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

Another night of above-freezing temperatures and light rain will prolong the dangerous avalanche conditions. Destructive and unpredictable wet avalanches running on deeply buried weak layers will be easy to trigger and may run naturally. Choose conservative, forested, low-angle terrain and avoid the runouts of large avalanche paths. 

Avalanche problems

  • Wet Slabs

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

    Practice conservative travel and avoid being on or near large, steep terrain features. Give yourself large margins of safety from potential runout zones. Wet slab avalanches can run further and break wider than you may expect. You may or may not see obvious signs, like whumphing collapses, before triggering an avalanche. Simply avoiding steep terrain is your safest option.

    A third night with above-freezing temperatures and some light rain will mean that these notoriously unpredictable wet slab avalanches are still likely. While temperatures will cool slightly by late Tuesday, we don't expect the slight cooling trend to improve stability by much. The weak snowpack structure proved problematic even with minimal warming and rain, and the prolonged warm period will only prolong the instability. There were observations of widespread very large wet loose and wet slab avalanches from near Harts Pass on Sunday, and avalanche professionals near Holden observed multiple very large natural avalanches on Sunday and Monday. We expect the snowpack to continue to weaken without significant cooling. There are two persistent weak layers: small facets buried on or around 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. Wet slabs may fail on any of these interfaces as water continues to drain through the snowpack.

    (1/27/2024)

    A natural wet slab avalanche that ran on Sunday near Harts Pass.

    Photo: Ryan Stoddard

  • Cornices

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

    There may still be lingering cornices that have yet to fail with the warm temperatures. Use extra caution near cornices while traveling on ridges, and make sure to give them plenty of space. During the last warm-up, there were reports of cornice falls that triggered deep avalanches. A natural or triggered cornice fall could be enough to gouge into these deeper weak layers, resulting in a very dangerous slide.

    (3/10/2022)

    An example of a very large cornice triggered avalanche.

    Photo: Matt Primomo

Avalanche Discussion

Wet slab avalanches are a tricky problem, and the best management strategy is to avoid steep terrain until temperatures drop below freezing. In other zones with a similar weak snowpack structure, avalanche activity has continued up to three or four days after peak precipitation. Multiple nights above freezing likely contributed to this prolonged instability. While East North has received less water overall, a similar pattern may occur up here. Especially as we head into our third warm night with little to no overnight refreeze of the snowpack. Even as natural avalanche activity seems to taper, these wet slabs could still surprise you, and the chance of you, a cornice, or a smaller avalanche triggering one of these avalanches remains likely. 

On Saturday, observers on Kangaroo Ridge reported a large collapse on the January 8th facets and audible natural avalanches in nearby terrain. On Friday, observers remotely triggered a very large persistent slab avalanche on an east aspect at 6,000ft in Leap Creek. Riders also triggered a small wind slab avalanche in Liberty Bowl near Blue Lake. An NWAC forecaster near Varden Creek (NNE, 5,400ft) found propagating test results on the early January facets in the middle of a shallow snowpack (65cm with HS 117cm). On Thursday, 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 the early January weak layer in the top 1/3 of the snowpack (50cm below the surface with HS 150cm).

On the 24th, NWAC forecasters traveled 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, a forecaster reported a number of small, loose dry and wet avalanches in very steep, craggy terrain. Warming temperatures moistened snow surfaces up to about 6,000ft on all aspects. 

Other recent observations pertinent to persistent slabs are:  

  • Another large cornice-triggered avalanche in Cutthroat drainage ran on a deeper weak layer, likely occurring on the 21st. Deeper crowns were 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.
  • Observers reported a couple of older D2.5 avalanches that ran on deeper weak layers near Hart's Pass, likely around the storm of January 17th. These occurred on an east aspect at 7,000ft and a west aspect at 5,800ft.

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

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