Bulletin d’avalanche

West Slopes South

Northwest Avalanche Center
Voir sur la carte

Danger d’avalanche

Tue
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
Open full map
Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

More sunny weather and warm temperatures will allow a springtime shedding cycle to continue on Monday. Once the snow surface has softened up and you are sinking into the snow past your ankle, it may be time to head toward shadier slopes.

Problèmes avalancheux

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    After a cool evening, temperatures will again start to climb on Monday, potentially reaching higher freezing levels than on Sunday. Expect wet avalanches to develop on steep sunny slopes as the snow surface starts to soften. Your first indicators that the upper snowpack is destabilizing will be rollerballs and pinwheels, snow shedding from trees and rocks, and the surface becoming wet and sticky. If you notice these signs, expect Wet Loose avalanches to follow and head toward shadier slopes. These slides often start at a point such as near trees or rocks, can entrain significant snow, and will fan out as they descend, possibly growing large and traveling long distances toward lower elevations. 

    We have multiple melt-freeze crusts and a layered upper snowpack. On slopes that see direct sunshine, this creates a potential point for pooling meltwater which could result in Wet Slab avalanches. You should use the same indicators and mitigation techniques as with Wet Loose avalanches. When in doubt, head toward shadier slopes.

    (4/11/2021) Rollerballs and snow shedding from rocks and trees were found near Crystal Mountain on Sunday 4/11 and are precursors to Wet Loose avalanches. They're a great indicator that it's time to head toward shadier slopes.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Slopes that do not see direct sunshine could still be harboring cold and dry snow, much of which may be wind-affected. Take a look for textured snow surfaces, or pillow-like piles of snow to help you identify wind-loaded slopes to avoid. They will be more likely as you ascend in elevation on slopes with a northerly tilt and often form near rocky features such as confined gullies or at the base of cliffs. You should also look for them on leeward slopes near ridgelines or on convex rollovers. You can use uptrack tests, hand pits, or test slopes to determine the slab potential on shady slopes and if blocks of snow are failing easily. If you find poorly bonded snow or suspect a terrain feature to be wind-loaded, you should seek out lower-angled options. 

    (4/11/2021) Wind textured surfaces, cornices, and smooth pillow-like piles of snow were observed near Crystal Mountain on 4/11 and can help you to identify wind-loaded slopes.

Avalanche Discussion

The snowpack around the West South is in a state of flux and both wet and dry avalanches pose a hazard right now. The 4/9 crust should be about 5-8" below the surface on slopes that typically see direct sunshine, or you could even find it on the surface in wind-exposed locations. On shadier slopes, this interface may present as more of a density break than a defined crust. As you look deeper in the snowpack, you'll come to the 4/7 interface which should be about a foot below the surface. This stout crust should exist on all aspects and be easily identifiable. We expect all avalanche activity on Monday to occur above the 4/7 interface, whether the avalanche has wet or dry characteristics. Avalanches have the ability to run far and fast on this crust and could initially fail at either interface. On sunny slopes, there may be a new surface crust that formed on Sunday night. Expect this crust to soften throughout the day and expose some of the layers outlined above.

Slopes on the northern end of the dial may hang onto a cold layered snowpack, and weak snow may exist at some of the interfaces outlined above, producing surprising avalanches. Multiple human-triggered avalanches have occurred on these layers in the neighboring Snoqualmie Pass zone recently, and two avalanche involvements occurred, including a skier who was fully buried. On slopes on the southern end of the dial, Monday will be a continuation of the springtime shedding cycle that started on Sunday when NWAC forecasters in the field observed Wet Loose avalanche activity and snow shedding from trees and rocks. The cycle will go through peaks and valleys over the next week as sunshine, freezing levels, and cloud cover fluctuate with the springtime weather. Choose safe travel routes far away from overhead hazards such as cornices or other large blocks of snow, and take into account your return route when planning your trip for the day.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

Régions couvertes