Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

The snowpack may need some time to adjust to the recent load it just received. On Wednesday, springtime weather could help to slow that process. So keep an eye on the snow surface, and if it is wet and heavy you should avoid slopes over 35 degrees.

Problemi valanghivi

  • Loose Wet

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

    This storm was generally wet and warm, which resulted in rain, mixed precipitation, and heavy wet snow at mid to lower elevations around the zone. On Wednesday, we’re going to add some dynamic springtime weather (sunshine) to the mix, which could help to weaken the recent storm snow and increase the likelihood of wet avalanches. Keep an eye on the snow surface as you travel throughout the day to see how the temperature and sunshine are affecting it in your area. You may be able to trigger a wet avalanche on any steep slope over 35 degrees where you find wet and sticky snow deeper than your ankle. These slides can entrain significant snow and grow large enough to bury or kill you as they descend, running far distances on a firm underlying crust. We expect the larger and more dangerous slides to occur above the rain/snow line or on the volcanoes where recent snow totals are deeper. But even smaller slides will be powerful with snow this heavy, so don’t get caught near terrain traps like gullies or cliffs, and be sure not to get pushed into a tree or rocks.

    (3/11/2022) Wet sticky snow like this lets you know the surface may be unstable and you should have wet avalanches on your radar. Photo: Dallas Glass

  • Storm Slabs

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

    The recent storm delivered several rounds of precipitation with fluctuating freezing levels. You will need to take a look at all of the recent snow for “upside-down” (heavy over weaker) snow on Wednesday. On the volcanoes, deeper snow totals were recorded, so obviously you will have more potential weak points and possibly larger slabs. Regardless of your location, expect slabs to be thicker as you ascend in elevation or in wind-loaded terrain. You can use small test slopes or quick hand pits as you travel to get a sense of how the snow has bonded and is reacting to your weight. Although we expect these slabs to heal relatively quickly, there is still plenty of uncertainty about their reactivity, specifically at upper elevations. They will be easier to trigger on steep features over 35 degrees or in wind-loaded terrain near ridgelines, confined chutes, or rocky features.

    (3/15/2022)

    Shooting cracks in the surface snow were found on 3/15 in the White Pass backcountry. These indicate that a slab is present and are one of the red-flag signs of instability. 

    Photo: Dallas Glass

Avalanche Discussion

The series of storms that have impacted the West South in recent days should wind down and leave us by mid-day on Wednesday. As of Tuesday evening, NWAC’s weather station at Paradise has recorded 2.75” of water from this event. Stations closer to the crest recorded considerably less, but still exceeded over 1” of water. As noted above, a variety of precipitation types fell throughout this storm as temperatures fluctuated over our large and varied zone. Crystal Mountain Pro Patrol reported that conditions became touchy as temperatures bumped up mid-day on Tuesday and a mid-storm layer about 4” below the surface became activated. Down at White Pass, avalanche professionals reported shallow slabs of a similar depth, along with some surface cracking in the new snow. 

On Wednesday, the snow’s sensitivity to triggers should rely heavily on how the weather pans out. If the snow “locks up” due to cooling temperatures overnight, the ability to trigger a wet avalanche in the morning hours should decrease. That could change as sunshine and springtime temperatures are forecasted to impact the zone later in the morning and into the afternoon. On the flip side, if a poor freeze occurs overnight then you might be dealing with these issues right off the bat. Look to the snow surface to help you determine the likelihood of avalanches and make travel plans that can help you avoid being in consequential terrain if the snow is wet and heavy. Avalanches may be difficult to trigger but could run a long way on firm crusts and greased paths if they are initiated, possibly gauging down to the Early March Crust.

On upper elevation northerly slopes, weak facets were identified just above the Late March Crust prior to this event. We do not have any information at this time about how these weak grains may or may not have come into play during this storm. If they survived and you trigger an avalanche on them, it has the potential to fail in surprising ways by breaking above you or spanning far distances. Tread lightly in these areas and let us know what you find out there by submitting a public observation.

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