Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Steep slopes with wind drifted snow are where you are most likely to encounter a slab avalanche on Saturday. Identify smooth, wind buffed surfaces or pillow-like piles of snow, particularly on convex slopes where triggering an avalanche is more likely. Avalanche danger is likely a step higher in areas with 10" or more of new snow or on slopes with active wind loading.

Problemi valanghivi

  • Wind Slabs

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

    Saturday should be a bit of a repeat with moderate westerly winds and another 2-4” of new snow in the forecast. Wind slabs will be easier to trigger where they initially formed over crust or weak, faceted snow and surface hoar. Hand shear and shovel tilt tests can highlight a weak interface below the latest storm and wind slabs.

    Scoured or eroded surfaces used to help determine the loading pattern could be hidden by light new snow that fell with less wind. Track the depth and stiffness of new snow layers as you gain elevation and switch aspects to help identify areas of wind slab. Look for and test freshly wind drifted features to get a feel for the reactivity of fresh wind slabs. When in doubt just steer around steep wind loaded features on lower angle and well supported terrain. 

    Rime and scoured surfaces helped us anticipate wind loaded slopes. 

Avalanche Discussion

Dry loose snow avalanches are probably the most common sign of instability you will see Saturday. Sluffs shouldn't grow too large - but keep an eye on how much snow is moving around or behind you if venturing into steeper terrain.

Heather Meadows picked up  6-8" of snow overnight with weather stations farther west and south seeing up to 1" of SWE equaling about 10" of new snow. Field observations were limited. Reported activity consisted of dry loose snow avalanches in terrain steeper than 40 degrees. A small human triggered wind slab was reported from the Baker BC on Thursday (obs).

It's been a full week since the last large human triggered avalanche. Four different D2 avalanches (three on Feb 8th and one on Feb 11th) are suspected of failing in a layer of weak facets or graupel buried on Feb 3rd. Two of these avalanches were either triggered from low on the slope or remotely. Given the time for layer interfaces to bond and the lack of recent avalanche activity , it’s unlikely - but not impossible - similar avalanches failing at the same interface will occur. A big load from heavy snowfall, rain, a falling cornice, or a smaller avalanche is more likely to wake up the layer in question.

 

 

 

 

 

 

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