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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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Monday may start sunny but increasing clouds and winds should dominate the weather pattern by day’s end. You may need to shift your attention from wet to dry avalanche problems as this occurs. Take note of actively blowing snow to help identify wind-loaded features to steer around. 

Problemi valanghivi

  • Wind Slabs

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

    There’s an east wind event headed for the West South, particularly near the crest. With cold dry snow already in place, increasing winds throughout the day should grow strong enough to easily transport it into shallow Wind Slabs on lee slopes. Due to the atypical wind direction, these slabs may form on aspects where you’re not used to seeing them. East wind events also often result in more mid-slope loading. Look for actively blowing snow as your easiest indication of aspects where slabs may be building. They’ll be more likely on convex rollovers and near rocky features such as the base of cliffs or confined chutes. If you suspect a slope is wind-loaded, simply avoid it by choosing another path.

    Further south, you may still encounter some lingering slabs from the storm that dropped multiple feet of snow on the volcanoes. While these may be trending toward unlikely, they could still fail on steep features over 35 degrees.

    (3/26/2023)

    A Wind Slab capped the recent snow and failed easily during tests on Mount St. Helens on 3/26.

    Photo: Keeley Rideout

  • Loose Wet

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

    The slow uptick in sunshine and temperatures will continue into Monday, maintaining the possibility of Wet Loose avalanches. It will be a race to see if there is enough sunshine to destabilize the surface before the easterly winds kick in and limit this avalanche problem. Further away from the crest or in areas where the easterlies have less influence, you could see more widespread wet avalanche activity. Keep an eye on how the snow surface is changing throughout the day due to solar input. If the snow is getting wet and sticky and you see new rollerballs or fan-shaped avalanche debris, head for shadier slopes. Be sure to stay aware of hanging blocks of snow such as cornices or glide cracks above you.

    (3/26/2023)

    Snow shedding from trees in the sunshine triggered tiny loose avalanches on a small slope.

    Photo: Andy Harrington

Avalanche Discussion

One could argue that this past weekend was more winterlike than spring around the West South zone. After receiving anywhere from 7 inches to 2 feet of snow at the end of last week, temperatures have been chillier than one would hope for this time of year. That has helped the new snow stay cold in many locations, but not all. Spring was able to pop up here and there to moisten the surface at lower elevations and produce wet avalanche activity on some slopes that see direct sunshine. You’ll likely encounter a new surface crust in these areas on Monday morning.

Last week’s snowfall is overlaying a melt-freeze crust on most aspects except high-elevation northerly slopes (3/22 interface). Storm totals increase the further south in the zone you travel especially on the volcanoes. On Sunday, avalanche professionals on Mount St. Helens found 2 feet of storm snow capped by Wind Slab. There were multiple density breaks within the recent snow. At the base, they found a layer of graupel above the 3/22 melt-freeze crust. At Crystal Mountain, NWAC forecasters found around 7 inches on top of the 3/22, highlighting the disparity in storm totals around the zone. Test results yielded some failures on the older 3/14 crust, including propagation during an extended column test. Shallow loose avalanches were triggered in the new snow on steep slopes. Over at Paradise, public observations relayed that cold dry snow still exists on shaded slopes, along with plenty of wind effect near ridgelines. Moist surfaces and rollerballs were reported by multiple groups on Saturday afternoon.

Be sure to check the bond at the 3/22 and the snow above it as you travel on Monday. The majority of avalanche activity is expected to occur at or above this interface.

Regioni coperte