Bollettino valanghe

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Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
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In sintesi

Another impulse of rain and wet snow are expected to create very dangerous avalanche conditions on Wednesday. Wet avalanches may run naturally and could be very large and destructive. Stay off of and out from underneath steep slopes while these conditions continue. 

Problemi valanghivi

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    2–3

    A prolonged period of warm and wet weather, combined with a weak snowpack structure have created unique conditions for scary wet slab avalanches. 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 drains through the snowpack. What does this mean? It means slides may fracture widely across terrain features, and carry the entire seasons snowpack with it. Slides may be 2-4ft deep, and could be powerful enough to take out trees. Along with these nasty slides, glide slabs, wet loose, slush and rock/landslides may occur. 

    Stay off of, and out from underneath steep slopes on Wednesday. 

    (1/27/2024)

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

    Photo: Ryan Stoddard

  • Cornices

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2

    If theres a cornice that hasn't fallen yet, it probably will on Wednesday. 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 deeper weak layers, resulting in much larger and dangerous avalanches. 

    (3/10/2022)

    An example of a very large cornice triggered avalanche.

    Photo: Matt Primomo

Avalanche Discussion

The last and final punch of moisture is incoming on Wednesday. Those areas where water hasn't drained too deeply into the snowpack are becoming fewer and fewer. As this occurs, wet avalanche activity is expected to increase. Really, the best management strategy is to avoid steep terrain and potential runout zones until the rain stops, and the snowpack refreezes.

We have little information on recent activity in the zone, as folks probably aren't going up into the mountains. As such, uncertainty in current conditions has increased. The zone saw a spike in avalanche activity on Sunday with very warm temperatures and rain. That day, observers reported natural slab and loose wet avalanches from Harts Pass. 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. 

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 (now wet 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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