Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

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

Keep an eye on how conditions are changing throughout the day on Wednesday. You may find that your primary avalanche problem shifts due to the weather or as you travel through terrain. If the snow surface is wet and sticky or you see new avalanches, its time to head for lower-angled slopes away from overhead hazards.

Problemi valanghivi

  • Loose Wet

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

    You could see a new round of wet avalanches as a result of solar input on Wednesday. Loose slides could occur if the sun is able to destabilize the newly fallen snow. Although they may start small, they have the ability to entrain snow and grow large as they descend, sometimes triggering slabs in the process. Be leery of steep slopes in the sunshine if you are sinking into wet or moist snow past your ankle or see new fan-shaped avalanche debris/rollerballs.

    Additionally, you should be cognizant of open slopes with overhead exposure to cornices, hanging blocks of snow, or crevasse-like cracks. Larger and more unpredictable avalanches could still fail in isolated locations so limit your time spent traveling in these areas.

    (4/8/2023)

    Rollerballs and a small Wet Loose avalanche from a sunny period prior to this storm. Note how these originated near rocky terrain.

    Photo: Andy Harrington

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    At upper elevations, Tuesday’s snowfall could have drifted into thicker pockets near ridgelines, rocky features, or convex rollovers. Look for textured surfaces or areas that look “fat” compared to the surrounding terrain to identify wind-loaded features where triggering a small avalanche is more likely. In isolated locations, they could entrain moist snow from below and start to increase in size. Use test slopes and hand-pits as you travel to check the bond to the old snow surface and how easily the new snow may be failing due to your weight. If the snow is failing easily in your tests, start thinking about the possibility of triggering slabs on unsupported convex slopes away from wind-effected terrain.

    (4/11/2023)

    A skier-triggered slab in the new snow on a convex slope in the neighboring Snoqualmie Pass zone. There was just enough energy and distance for the slide to start to gouge down into moist snow below.

    Photo: Andy Harrington

Avalanche Discussion

The snowpack around the West South zone has been through a lot in recent days. Springtime weather has resulted in roughly 2-3 inches of precipitation (SWE) since Saturday afternoon, most of which was rain. Rain was replaced by snow on Tuesday when anywhere from 5-8 inches is estimated to have fallen throughout the zone. 

On Monday, Crystal Mountain Pro Patrol reported triggering multiple very large (D2.5-3) Wet Slab avalanches and easily triggered Wet Loose avalanches during their mitigation work. Similar loose avalanches were reported by patrol on Tuesday morning. They also noted that the cooldown and return to snow were not enough to stiffen up the moist snow from days prior.

Further south in the zone, scientists from the USGS on Mount St. Helens recorded up to 5 large to very large natural avalanches with their seismic equipment during this stormy period. White Pass Pro Patrol reported natural activity in the surrounding backcountry and was able to trigger loose avalanches with ski cuts.

Although it is undoubtedly Spring out there, we’re still in a state of transition away from our wintertime snowpack. Under the surface, cold layered snow still exists and this week should be unseasonably cold for April. You’ll likely encounter periods of sunshine, snow showers, and rain all in the same day as you travel through the mountains which can lead to a myriad of avalanche conditions for you to unpack. On Wednesday, you’ll likely encounter higher accumulations the further south in the zone you travel, specifically on the southern volcanoes.

Regioni coperte