Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

The storm parade will continue in the West South on Monday. This next wave should bring a change in wind direction and overlapping avalanche problems. Keep your plans simple by giving yourself plenty of terrain options and defaulting to slopes under 35 degrees.

Problemi valanghivi

  • Storm Slabs

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

    Continued snowfall Sunday night and Monday will increase our storm totals and create the potential for additional weak interfaces. Springtime temperature swings and gusty winds could also create problematic layers within the recent storm snow. To this point, most of the storm snow has reportedly been fairly low-density but these environmental factors could change that. Take the time to look at all of the snow over the 4/8 crust to determine if an upside-down snowpack has developed (where heavy snow exists over lighter, weaker snow). In addition to digging, you can use small test slopes to check how the snow is reacting to your weight. Visual clues like cracking of the surface or blocks of snow failing in upslope tests while you travel can help key you into the snow’s slab potential. If you find that slabs exist or the snow is failing easily during your tests, avoid slopes over 35 degrees where triggering an avalanche is more likely.

    (4/10/2022)

    A mid-storm density break near White Pass was highlighted by snowpack tests on 4/10.

    Photo: Dallas Glass

Avalanche Discussion

The snow is just going to keep on coming for the West South zone. NWAC weather stations and on the ground observations indicate that storm totals in many areas have already exceeded 2 feet. On Monday, the southern half of the zone will again be in the bullseye, but most areas further north should still receive plenty of additional snowfall above the 4/8 melt-freeze crust.

On Sunday, NWAC forecasters near White Pass reported low-density storm snow with some small (D1) Wind Slabs triggered near ridgelines and a reactive density break about a foot below the surface. Similarly, Crystal Mountain Pro Patrol reported plenty of powder snow and Dry Loose avalanches as a primary concern. Observations from upper elevations or on the volcanoes were limited due to the ferocity of the storm, but we expect higher snowfall totals and more wind effect in these areas. On Saturday, drifts as large as 3 feet were already building on Mount St. Helens ahead of the bulk of precipitation and wind. 

On Monday, a change in the storm pattern could result in some different conditions around the zone. First and foremost is a switch in the wind direction toward East. While we’re not anticipating a full east wind event like we often see during the winter, these winds could be locally strong in some areas, particularly near the crest. They could easily redeposit the low-density storm snow onto aspects you’re not used to seeing loaded by the wind. In addition, this could create the upside-down snowpack we mentioned above. 

Rising daytime temperatures is another way we could achieve heavy over lighter snow. We’re not expecting full sun or anything close to it, but even a slight bump in temperatures could help the snow “slab up”. It could also kick off some loose avalanches on steeper slopes. With so much recent storm snow, these avalanches could be large enough to be consequential, particularly when a terrain trap is involved. Depending on the amount of warming and solar input, loose avalanches could cross the threshold from dry toward wet fairly quickly. In areas where cold dry snow is not affected by the wind or springtime temperatures, Dry Loose on slopes over 35 degrees could be your primary avalanche problem to manage on Monday.

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