Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Mon
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

Wind speeds should increase in the afternoon ahead of the next storm and build fresh slabs of wind drifted snow at upper elevations. Avoid steep slopes where you observe active wind loading. Evaluate the bond of new snow layers anywhere you find more than 8" of new snow over crust or other old snow surfaces below.

Problemi valanghivi

  • Wind Slabs

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

    Wind transported snow was reported with moderate winds Saturday afternoon with a handful of large wind slab avalanches in exposed terrain. Higher wind speeds Sunday afternoon ahead of a powerful storm will step up transport and slab formation at upper elevations. Older wind slabs from Friday night’s storm could still be in play as well.

    If you trigger a slab it would likely be on a leeward slope just below ridgeline, or on a terrain feature like a convex rollover or gully wall. Look for blowing snow, changes in snow consistency, or visual clues like wind-scoured ridgelines and cornices to identify and help you avoid steep slopes holding wind slab.

    Take a few minutes to investigate the bond of new slabs to what’s below whether it be slick crust, less dense snow, or maybe even a thin layer of facets or surface hoar. Small test slopes can help gauge reactivity and how slabs will respond to the weight of a person. Hand pits might show a stronger layer sliding easily on a weaker layer. 

     

    (12/29/2022)

    Blowing snow and sharp wind lips above a freshly formed wind slab.

    Photo: Dallas Glass

Avalanche Discussion

With a transition to warmer temperatures wet loose avalanches are more likely at lower and mid elevations, regardless of the amount of sun. Also, the larger-than-average cornices that formed this winter will start to sag and get primed up to come crashing down and lay waste to anything in their path. Keep track of what is above you be it a large cornice or steep slopes producing rollerballs or other signs of wet avalanche instability. It's up to you to stay out of the way.

Observers in West North reported numerous natural and human triggered slab avalanches in areas that saw snowfall and wind speeds above what was forecast. Though small in size slabs were reactive into the afternoon. Avalanche mitigation work to protect Hwy 2 in Stevens Pass produced a handful of avalanches.  Also some very large natural avalanches of a different character were reported from the same zone. Check out this forecast for more information.

An unexpected 4-8" of new snow fell in parts of West Central. Snotel sites reported total precipitation since Friday morning at 0.5" to 0.75" with White Chuck picking up about 7" of new snow in the same time period. Similar amounts of new snow fell in West North with 6" in Snoqualmie Pass and a few inches of new at Stevens.

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