Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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In sintesi

Even though the danger is Low and conditions are generally safe, you may find you can trigger small wet avalanches. If you see new rollerballs be leery of similar slopes.

Problemi valanghivi

  • Loose Wet

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

    Even in this warm pattern, the biggest creator of wet snow will be the sun. Any surface receiving direct sunshine should soften during the day. If more clouds hang around than expected, the weather could feel very hot and muggy. This “greenhousing” effect may cause wet snow to form no matter the aspect. In both cases, shallow spots in the snowpack especially near cliffs and rocks will be most susceptible to warming. Watch for new rollerballs as your primary clue that the surface is becoming wet and unstable. When you see this observation, be leery of similar slopes. 

    We expect any loose wet avalanche on Thursday to remain small and isolated. However, as we head deeper into this prolonged warm-up it becomes harder to predict how the snowpack will react. This is particularly true for areas near Crystal, Mt Rainier, and White Pass where more snow from the end of January sits over a firm crust. If you see natural avalanches or slides start to entrain snow, the snowpack  passed its tipping point and the danger is on the rise.

    (2/9/2022)

    Triggered rollerballs on an E-facing slope. This is a great sign that the snow surface is becoming wet and unstable. 

    Photo: Andy Harrington

Avalanche Discussion

The avalanche hazard has been Low around the West South for several days. However, even though the danger remains the same, a lack of cloud cover and high freezing levels may cause slides to be easier to trigger on Thursday. This is a very large forecasting zone with lots of variability in the terrain. Overnight it’s likely that some locations will remain cloudy limiting the snow’s ability to freeze. In other locations, clear skies will help form a very strong surface crust. As a result, the overnight cloud cover could significantly impact the snow conditions (and possibly avalanche danger) you encounter. 

On Thursday, very warm and sunny weather should soften all slopes. Moderate to strong winds may curtail the thawing on exposed areas, but eventually, the heat should win. On Wednesday, an NWAC forecaster in the White Pass triggered large rollerballs and a very small loose wet slide on a due East aspect. This highlights the changing of the seasons. As we move further into February, the sun will start to reach further around the compass dial and impact slopes that have remained shaded all winter. 

Over the past few weeks, strong wind events, sunny days, and melt-freeze cycles created a wider variety of snow surfaces and a more aspect-dependent snowpack. On more southerly slopes, a spring-like snowpack exists. While you may find dry snow just under the surface, melt-form grains dominate. These slopes are occasionally icy or have a breakable crust. In shaded terrain. A wider variety of surfaces exist. Wind-scoured icy slopes, breakable crusts, and even isolated pockets of soft snow can be found. It’s on these aspects you can still find the Late January Facet-Crust layer. We’ve been talking about this potential weak snow for over a week now, but it’s still on our minds as we head deeper into this warm period. A layer of sugary facets sits sandwiched between two crusts at the base of storm snow from the end of January. Around Mt Rainier and White Pass, this is a foot or more deep. Further south, near Mt St Helens and Mt Adams, this may be only a few inches below the surface. So far we have not hear of any avalanches on this layer in the West South zone. How will this layer react to the increasing temperatures? Hard to say, but it's worth keeping on your radar. Below the Late January Crusts, a very strong and spring-like snowpack exists. We are not tracking any layers deeper in the snowpack.

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