Bollettino valanghe

East Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
4 · Forte
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In sintesi

Significant snow and strong winds are forecast for Sunday night and Monday. Avalanches may run naturally, and it will be very easy to trigger avalanches large enough to bury or kill you. Avoid travel in avalanche terrain, avoid areas with large snowdrifts, and steer clear of open bowls where avalanches may run from above.

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Very Likely
    Dimensione
    1.5–2.5

    A Pacific Northwest storm with a good fetch of moisture is just beginning to impact our region Sunday evening. This new snow will be falling on various weak surfaces that may easily produce large slab avalanches. These weak surfaces exist at all elevations, and you can likely trigger avalanches in steep terrain, even in sheltered locations at lower elevations.  Strong winds will build larger and more dangerous avalanches on lee aspects at upper elevations. Avoid travel in steep terrain on Monday and stick to sheltered low-angle slopes. Avalanches may break surprisingly wide, give extra room for runouts of large avalanche paths in alpine areas. 

    Hand pits and small test slopes can give you excellent feedback about how the new snow is bonding to the existing snow surfaces. Monday will be a great day to observe red flags indicating unstable snowpack conditions like recent avalanches, shooting cracks, and collapsing. 

    (12/25/2021)

    Example of storm slab propagation in wind-stiffened snow below treeline.

    Photo: Ron Martin

Avalanche Discussion

A winter storm impacting the region Sunday night will quickly deteriorate current snowpack stability. Up to 2 feet of snow may fall in areas throughout the East South zone by the end of the day on Monday. More snow is expected in locations closer to the Cascade Crest and in the southern portion of the zone. However, even areas far East of the crest may receive 12 inches of snow. Many of these eastern areas may still have shallowly buried obstacles, and the deepest snowpacks are around Mt Aix and Bumping Ridge. Areas with deeper snowpacks will have the potential to produce larger avalanches. 

While observations in East South are limited, there have been observations of weak snow on the existing surface in adjacent zones. Underlaying the weak snow is a variety of surfaces, from sun crusts and wind crusts to soft snow. As a result, adjacent slopes and slight variations in aspect may react very differently to the new snow. We are particularly concerned about steep solar aspects with a few inches of preserved stellar snowflakes, surface hoar, and faceted crystals. On these slopes, avalanches may break farther and become larger than a typical storm slab. 

While most observations have indicated a good bond between the upper snowpack and the Solstice crust, now buried 2-3 feet below the surface, some surprising avalanches in other zones have occurred on this layer. This uncertainty, along with the potentially high consequences of these very large avalanches, warrants extra caution as smaller avalanches may step down to deeper interfaces. 

If you get out to ride, ski, snowboard, snowshoe, or otherwise recreate in the snow, use our observation page to let us know what you see. 

 

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