Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

East winds could result in a fresh round of wind slabs for you to manage on Monday. Avalanches of varying sizes have been reported every day this week. Consider the possibility of very large avalanches on big open slopes and talk with your partners about your travel plans and acceptable level of risk. 

Problemi valanghivi

  • Wind Slabs

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

    Another east wind event is headed our way on Monday. It shouldn't be as intense as what we experienced earlier this weekend. Similar to Saturday, areas near the crest or a mountain pass are prone to the windiest conditions and, therefore, slab development.  East winds often result in more mid-slope cross-loading and reverse loading, creating slabs in locations you're not used to finding them. They could be fresh, a few days old, or even layered on top of each other. Look for actively blowing snow, textured surfaces, or fresh drifts behind objects to help determine wind-loaded features to avoid. If you're traveling over firm snow that feels hollow, you may be on a wind slab. Convex rollovers, the base of cliffs, or the sides of gullies are all popular places for wind slabs to form. Small test slopes can give you an idea of how sensitive they may be.

    (1/14/2024)

    Intentionally triggered wind slabs near ridge crest. N, 6700ft. White Pass backcountry. HS-ASc-D1-R1-S

    Photo: Dallas Glass

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    This is the problem that should be shaping your travel plans.  We’ve been talking about weak layers in the snowpack for a while. These layers have come to life this past week as natural and explosive-triggered slides propagated widely and wrapped terrain features. This isn’t a problem you can tiptoe around. We’ve found a poor snowpack structure everywhere we have dug a hole in recent weeks. The question mark is not about size or distribution but the sensitivity to triggering. Many of these avalanches failed with relatively small triggers, in some cases humans. It may take something bigger, such as a step-down, cornice, or explosives, as we move forward. That's not a sure bet, however. You will likely not see any red-flag signs of instability before one of these slabs fails. You should consider staying off big open slopes where triggering an avalanche on this layer would result in a slide that would likely be unsurvivable. 

    (1/13/2024)

    Another very large explosives triggered avalanche at Crystal Mountain. There have been several of these this week with crown depths of roughly 3 feet. This one is on Threeway Peak.

    Photo: Crystal Mountain Pro Patrol

Avalanche Discussion

A fair weather day with moderating temperatures and little wind allowed backcountry enthusiasts to return to the mountains. At White Pass, an NWAC forecaster observed natural wind slab avalanches and plenty of wind effect as he investigated our deeper layers of concern.  On Saturday, the Mount Rainier Nordic Patrol and backcountry travelers near Crystal Mountain relayed a similar story. We have received an avalanche observation from our zone every day since 1/6, indicating what kind of week it's been. 

We do not have any observations from the southern volcanoes. We do know the storm carried on longer down there, and large wind slab avalanches occurred in the early morning hours on Sunday in the neighboring Mt. Hood zone. If you're traveling down south, you may want to take a peak at the Hood forecast to get a feel for conditions. 

Speaking of our deeper layers of concern (the 12/30 and Solstice Crusts), they're roughly 4 feet deep in many areas of the zone and are not showing much in the way of improvement. They are still producing concerning test results and large to very large avalanches (D2.5-D3) when tested with explosives by the Crystal Mountain Pro Patrol. At least three notable explosives-triggered avalanches occurred on Saturday. Just outside the ski area's boundary, backcountry travelers discovered a crown of a natural avalanche roughly 3 feet deep. We do not know what day this avalanche failed, but it was within the last week. We also have reports of deep and widely propagating avalanches at White Pass and Paradise during this past week.

On Monday, areas not impacted by the easterly winds should have a fair weather day as temperatures rebound closer to seasonal norms. If you find yourself far west of the crest, say on Mount St. Helens, you could even see a few rollerballs as the sun warms the snow surface. 

 

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