Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

You can trigger a large and potentially surprising slab at typical start zone elevations and above. Fresh, reactive storm snow combined with wind loading will strain an interface about a foot below the snow surface. Choose supported slopes less than 35 degrees at upper elevations and anywhere you experience signs of instability such as whumphs or shooting cracks.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    We're concerned about the upper snowpack structure as we continue to load it up with fresh snow and wind. A harbinger small, natural slab avalanche (featured right) combined by reports of widespread whumphing tells us we're dealing with a touchy interface. Winds and temperature fluctuations have created a slab on top. Another 6-7" of snow over the next 24 hours with moderate winds will accentuate instabilities on wind-loaded terrain, but with the snow structure in place, you can trigger a slab avalanche on any aspect. We think that milder temperatures below 5000 ft or so have helped to accelerate the healing of problematic interfaces at these elevations. But slopes above around 5000 ft will be far less forgiving. Friday will be a good day to step back and seek supported slopes less than 35 degrees that don't have typical signs of wind loading (overhanging cornices, lens-shaped pillows, or active snow transport). Whumphs, shooting cracks, or evidence of recent natural avalanche activity confirm the problem in your terrain.

    If you're keen to investigate the problem further, dig down to the 12/30 interface which may have a layer of weak faceted snow sitting over a stout crust.

    (1/4/2024)

    A small, natural that potentially ran within a layer of facets preserved above a stout crust.

    Photo: Daniel Cope

Avalanche Discussion

Backcountry travelers and Baker Pro Patrol reported a poor bond between the 4-6" of snow that fell Tuesday through Wednesday and 4" of snow that buried 12/30 crust and then faceted under several clear nights.  Although Baker Pro Patrol found Thursday's problems healing by Friday, the situation in the Backcountry was quite different with a reactive interface about a foot down. This is concerning given the minimal loading (2-3" of snow in the last 24 hours) and cooling temperatures which normally would help to strengthen a slab. It has us thinking that the current snowpack will not react well to additional stress from snow and wind on Friday; and a larger event Friday night into Saturday.

That slab conditions hadn't yet developed by Tuesday. A few wind-loaded features would produce cracking and shed small blocks when kicked, but slab formation was too isolated to be a problem in the Baker Backcountry.  Further east in the zone, wind slabs were more reactive at middle and upper elevations in Sibley Creek where stronger winds were observed. It is likely that these slabs are quickly gaining strength given the recent mild temperatures.

Below the firm melt-freeze crust crust, all layers are well-bonded and consist of crusts, melt forms, or rounded grains. Snowpits at mid and upper elevations have repeatedly shown a well-consolidated snowpack with no layers of concern.

Regioni coperte