Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Wed
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In sintesi

Heavy wet snow on Monday fell over cold dry snow from the weekend creating an upside-down snowpack around the West South. You may still trigger avalanches at the base of the new snow especially on steep convex rollovers and in more complex and rocky terrain. In locations that received more 10” of new snow, these avalanches could become large enough to bury and kill you.

Problemi valanghivi

  • Storm Slabs

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

    New and reactive storm slabs formed on Monday as heavy wet snow fell across the West South zone. One avalanche professional in the Crystal backcountry reported several shallow natural and human-triggered slabs. You may still trigger these potential avalanches on Tuesday around steep convex slopes and in rocky and complex terrain. Small test slopes and quick hand pits can give you insights into how these slabs may react. If your test slopes fail or hand pits find layers that break easily, steer around nearby slopes greater than 35 degrees. 

    Locations on and near the volcanoes may have accumulated more than a foot of snow on Monday. In these areas, avalanches could become larger and more dangerous. Approach any steep slope with caution until these recent storm slabs have time to heal.

    (12/19/2021)

    Using simple hand pits while you travel is a quick way to gain some information about slab potential and the depth of potential weak layers in the upper snowpack. 

    Photo: Dallas Glass

  • Loose Wet

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

    Rain began falling below treeline on Monday afternoon in some areas of the West South. Continued light rain and warming temperatures will create a wet snow surface for most locations. As a result, don’t be surprised if you see or trigger small loose wet avalanches at mid and lower elevations Tuesday. Wet heavy snow and new rollerballs may serve as your best clue that you can trigger one of these avalanches. Even though they should remain small, don’t let them push you into an open creek or over exposed rocks. In areas that remain drier overnight, the loose wet avalanche hazard may not materialize.

    (12/20/2021) Example: These rollerballs occurred on Monday afternoon near Mt Hood because of rain on snow. Photo:  Andrew Kiefer

Avalanche Discussion

Despite the varying new snow totals around the West South zone, the upper snowpack structure should remain largely similar. Heavier and wetter snow from Monday sits on top of weaker snow from the weekend. The only real difference from one location to the next seems to be the potential size of any avalanche. Rain on Saturday fell to around 5600-5800’ in many areas and formed a new crust layer in the snowpack. Above these elevations, a firmer layer of moist snow was observed. We expect any avalanche activity to remain above the top of this crust/firm snow interface (12/18). 

Regardless of the similarities, the West South is a very large zone with distinct mountains and weather patterns. It is still early season and we have lots of questions about the snowpack. Even as the danger rating slowly drops on Tuesday, this uncertainty sits at the forefront of our minds. Before you commit to larger and higher consequence slopes, take time to gather information and see if the conditions you observe match with what you expected. If they don’t, dial it back and seek out lower angled and less consequential terrain. You can help us fill in the gaps. If you’re out in the mountains near Mt Adams, Mt St Helens, Mt Rainier, Government Meadows, White Pass, and Crystal Mt let us know what you find by submitting an observation. 

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