Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Even though the storm is winding down in the West South, this was an abrupt change to the snowpack. Avalanches could trigger easily especially near and above treeline and in wind-loaded terrain. Seek out lower angled and less wind affect slopes to give the snowpack time to adjust.

Problemi valanghivi

  • Wind Slabs

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

    Backcountry travelers easily triggered wind slabs along the lee sides of ridges on Monday. These slides often failed at the base of the new snow and slid on the firm icy crust below. While many of the wind slabs triggered on Monday were small, they often failed the width of the feature in small terrain. That can be a clue that, bigger slopes could produce much bigger avalanches. Conditions will likely be similar on Tuesday. It will take more time for these slabs to bond to the underlying hard snow. So, look for clues like drifts and wind-textured surfaces to help anticipate which slopes and features hold wind-loaded snow. Then choose lower angled or less wind-affected terrain to avoid the hazard.

    (1/31/2022)

    This small wind slab was intentionally triggered by a skier on a NE aspect around 6300'. The avalanche failed at the new-old snow interface. HS-ASc-R1-D1-I. 

    Photo: Shane Robinson

  • Storm Slabs

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

    At lower elevations, the warm start to the storm likely helped the new snow “stick” to the old surface. However, that may change as you enter the near treeline band. A variety of weak snow surfaces and icy crusts were reported prior to this storm and now the new snow sits on top (see discussion for details). You may see that avalanches fail at the base of the new snow or on layers created by the storm. While you can use small slopes and hand pits to investigate the recent snow, this complex variability could make predicting how any particular slope reacts extremely difficult. Instead, this could be a good time to take a more conservative approach and give the snowpack time to heal. At mid-elevations, you can use smaller and lower consequence terrain to help manage this uncertain snowpack until we know more about how these layers fared during the storm.

    (1/28/2022)

    Large surface hoard and small near surface facets were seen on a variety of slopes in the Crystal backcountry. These grains were typically seen on NW-NE aspect, but could be found in any shaded area.

    Photo: Dallas Glass

Avalanche Discussion

While this wasn’t a huge storm by Cascade standards, it did bring respectable snowfall totals to many locations of the West South zone. Even though snow showers are decreasing, some areas could see a few more inches accumulate before Tuesday afternoon. Winds during this storm were very strong and gusty. Even more wind-sheltered sites like Paradise and Sunrise recorded many hours of sustained moderate to strong winds.  Expect the new snow to be redistributed at mid and upper elevations often with erratic loading patterns. 

Prior to this storm, numerous observations recorded near-surface facets, facet-crust sandwiches, icy crust, and surface hoar across the zone. In general, firm crusts were found on more southerly aspects, while facets and facet-crust combos were seen on shadier slopes. However, most often “variable” was the word of choice to describe the surface. Because these layers are relatively shallow, they should be easy to observe with simple observations as you travel. However, the variability will make decision-making uncertain. 

Fortunately, below this most recent interface, the snowpack is very strong and well settled. Currently, we don’t have any significant layers of concern deeper in the snowpack. We expect any avalanches to occur near or above the 1/30 interface.

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