Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

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

In sintesi

Happy new year!

A brief pulse of wind and snow will create the potential for avalanches on wind-loaded slopes, especially at higher elevations. Shifting winds could drift a slab onto exposed slopes near ridgelines, below cliffs, and on the sidewalls of cross-loaded gullies. With good visibility in the forecast, watch for blowing snow and pillowy drifts, and give a wide margin where these signs are present.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Though the precipitation totals aren’t too impressive, there is still snow available for transport and we expect new slabs to build overnight and in the morning hours. Wind slabs are most sensitive when they are fresh. To add to the uncertainty, we have received widespread reports of weak surfaces which could heighten the reactivity of any new slabs. Steep unsupported terrain and convex roll overs are especially suspect. Though potential avalanches should be confined to the new snow, terrain traps would heighten the consequences of being caught in even a small slide. Your eyes will help you identify slopes with wind-transported snow. Up-track tests, representative and safe test slopes, and hand pits can all help you gauge the behavior of a potential slab. Check for snow and slab depth frequently and expect this problem to be more sensitive at higher elevations and anywhere you find a deeper drift. Away from wind-exposed slopes, you’ll find lots of fresh snow and fun riding conditions.

    (1/9/2021) Pillowy drifts, cross-loaded gullies, cornices, and a wind-slab avalanche on a convex roll. Any one of these is a signal of a slope to avoid on Wednesday.

     Photo: Pete Durr

Avalanche Discussion

Increasing wind speeds moved into the West South on Tuesday afternoon ahead of a weak weathermaker. The wind will be more of a story than the precipitation for many parts of the zone, though the volcanoes should see more significant accumulations. In the non-volcanics, we are multiple days out from significant accumulation or wind, and we have received widespread reports of a largely non-reactive snowpack. As a result, we expect any activity on Wednesday to involve new wind slabs. How reactive they are will largely depend on where you are in the zone, how the wind behaves, and what is on the surface before these new slabs form.

Surface hoar and near-surface facets can become an issue if they are buried intact. While we form tons of surface hoar in WA, high wind speeds often knock it down before the next event comes in. This system is relatively small and the wind speeds don’t look too impressive. If weak surfaces are preserved, any subsequent slabs can propagate further and wider than you might expect. While this isn’t cause for alarm yet, it is on our radar going into Wednesday and it should be on yours as well. You can try and dig to look under the snow, but these crystals are small, sometimes spotty in distribution, and typically hard to identify, so your safer bet is to use other tools to gauge for reactivity, or give wind-loaded slopes a break while we all assess the bond of the new snow.

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