Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The storm snow is settling, but you could still trigger an avalanche on some slopes that have yet to heal. Look for signs of instability like cracking as you travel. Ease into terrain, and evaluate each slope separately because of the lingering possibility of buried surface hoar. 

Problemi valanghivi

  • Storm Slabs

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

    Warming temperatures and sunshine is helping to settle the storm snow. Howevver, slabs involving the new snow could still be triggered, especially if they rest on buried weak layers like surface hoar, facets or crusts. Look for signs of instability like cracking and recent avalanches as you travel and make your terrain choices accordingly. Very steep and unsupported terrain may be the most likely place to trigger a small soft slab. Avalanches could be 1-1.5ft deep, especially in areas that have received wind loading in the past few days, like near ridgelines. Buried surface hoar is 'spatially variable' in that you may find it on some slopes but not others, even if they are the same aspect and/or elevation. 

    You may also be able to trigger small loose slides, both dry and wet on steep slopes. If you notice the snow can entrain on steep slopes, or observe rollerballs and moist sticky snow, then expect this problem.

    Example small storm slab that release beneath a cornice.

Avalanche Discussion

Observers on Sunday found fast and clean shears beneath the new snow, 8" down on a shaded, sheltered northerly aspect near Arrowhead. They also observed some wind affected snow in the Henry Creek clearcuts, but slabs were generally unreactive. Warm temperatures have substantially helped to settle the new snow. Stevens Pass picked up 0.75" of SWE with about 11" of snow on Saturday. This was somewhat unusual, in that the passes should received less snow and water than areas further east. Observers were finding a layer of buried surface hoar that sits underneath a very thin zipper like 'drizzle crust' on the pass from earlier in the week. On Friday, I found a few areas where previous wind drifting had overlaid slabs on this layer. In areas with some wind stiffening, I was able to get fast and clean fracturing. The failure layer often involved buried surface hoar, just underneath the thin crust. Look for surface hoar under the surface on open, but wind-sheltered slopes. This layer could be 8"-18" deep on Monday.

Layers of weak snow and crusts were buried by a series of storms in mid to late November. This layer is now near the ground, and has been observed to be gaining strength and rounding. These older layers generally haven't been a problem for avalanches in this zone as much as in the East Central zone, though it's something to consider, especially in true alpine terrain. Remember, the snowpack may still be hiding shallowly buried hazards of rocks and stumps, especially at lower elevations. Let us know what you see by submitting an observation!

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