Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Avalanches in wind drifted snow, whether fresher drifts or older, harder, drifts, are your largest concern on Sunday. As you gain elevation, larger amounts of newly fallen snow and wind-effect occurs, and likelihood of triggering an avalanche increases. Identify where wind formed denser slabs of snow and steer around these features on steep slopes.

Problemi valanghivi

  • Wind Slabs

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

    A variety of old, stubborn, wind slabs likely exists through much of the zone. The layers have mainly been found to be unreactive, however on large upper elevation steep slopes they could still produce an avalanche with the weight of a person. About 6 inches of snow is forecasted to fall by the end of the day Sunday, and your avalanche problem is expected to shift more towards the new snow layer. As many old surfaces at mid to upper elevations firmed up in the last few days, you should easily be able to tell the depth of the new snow layer. In areas where you see active loading, or find thicker deposits of new snow, you can expect to trigger a slab avalanche.

    Expect loading to occur in more common areas, such as along ridgelines, in gullies and on convex rolls, unlike the larger old slabs which developed in less common places with unusual winds. Paying attention to the feeling of snow beneath you is important during the day. Feeling for stiffer, hollow layers beneath you is a key area to avoid old slabs. As for the softer new slabs on top, pay attention to thicker new snow deposits and avoid these locations on steep slopes, especially when they begin amounting to 6 inches or more. 

    Another important factor to be aware of is that weaknesses, most notably surface hoar, developed in the last week. This could mean that newer, shallower, slabs could pop off easier than expected in sheltered areas where it was not destroyed by wind. 

    Subtle new wind slabs like this one could become a problem as more snow falls throughout the day. Photo: Joe Dellaporta

Avalanche Discussion

Snowfall amounts could be larger than expected from the Mountain Loop Highway and further south. Where more snow falls, expect larger avalanches that will be easier to trigger.  A variety of wind slabs could be found during your outing Sunday. Your challenge is identifying the different layers and avoiding them in areas where they could produce avalanches. A shallow, soft coating of surface snow could hide variable, crusty layers beneath. Wind-protected, shady slopes are where you might still find nice low-density snow, however, this is where surface hoar likely exists on the old snow surface and new snow avalanches could easily be triggered. 

Buried surface hoar and deeper crust-facet layers still lurk in the middle and lower snowpack in some areas. No new avalanches related to either of these layers have been reported this week despite extensive backcountry traffic. Heavy loads might produce a large avalanche in any of these weaker layers. A big load of new snow or rain from a future storm might also wake up these layers and produce very large natural avalanches.

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