Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A quick moving storm will bring modest amounts of new snow and periods of strong wind. The danger of triggering a slab avalanche will increase on Thursday, especially at upper elevations. Avoid steep terrain where you suspect wind has deposited new slabs of dense snow.

Update @ 6:17:  BTL + NTL danger rating increased due to moderate to strong winds lasting longer into the morning and potentially more snowfall than expected. 

Problemi valanghivi

  • Wind Slabs

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

    Expect to see new wind slabs on Thursday with potentially dangerous conditions developing in the alpine. Fresh wind slabs will once again build on leeward slopes. There is enough new snow  (5-10 inches by midday) to resupply the dwindling stock of light density snow available for wind transport. Identify areas of wind slab using visual clues like wind scoured snow surfaces and cornice features that point in the direction of wind loading. Poor visibility may make it difficult to identify wind loaded slopes in the morning - err on the side of caution when traveling near avalanche terrain and build this uncertainty into your plan for the day.

    Periods of intense snowfall could also build soft but very reactive slabs in even wind sheltered terrain, especially where accumulating on a weak snow surface. Use hand shears and other simple tests to evaluate the bond of new snow layers to the old snow surface below. Avoid areas of unstable snow in steep terrain with tree wells, open creeks, or gullies in the track or runout.

    (12/29/2021)

    Small wind affected feature on Shuksan Arm showing both wind erosion and loading in close proximity.

    Photo: Lee Lazzara

Avalanche Discussion

Clear skies and cold temperatures dominated the West North after nearly a week of steady snowfall before and during Christmas. Despite receiving 5' feet of snow in favored locations, most avalanche activity since December 21st was limited to shallow, human triggered storm and wind slab avalanches.  Varying winds the last few days created new, small wind slabs on a variety of aspects. More noteworthy observations include two large avalanches triggered during avalanche mitigation work and some large natural avalanches in alpine terrain. These were likely part of a natural avalanche cycle during the period of extended snowfall. These outliers - on Mt. Shuksan and a few others in more distant parts of the Cascades -  indicate that layers deeper in the snowpack like the Solstice crust are still in the back of our minds when it comes to upper elevation terrain. While triggering such an avalanche is unlikely, it's not impossible in extreme terrain or with a large trigger like a smaller avalanche or cornice falling from above.

 

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