Bulletin d’avalanche

West Slopes South

Northwest Avalanche Center
Voir sur la carte

Danger d’avalanche

Tue
Alpin
3 · Marqué
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

The snowpack is beginning to heal after an intense storm cycle. Choose slopes under 35 degrees where you find the surface snow wind affected or becoming wet. Several very large slabs released naturally over the weekend highlighting the fact that we still have a deep slab problem. Avoid travel on large open slopes near and above treeline and limit your exposure to large avalanche paths while traveling at lower elevations.

Problèmes avalancheux

  • Wind Slabs

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

    Recent strong west winds easily transported snow, sculpted the snow surface, and formed slabs near and below ridgeline and occasionally even in the trees. Milder weather Sunday and Monday will allow these slabs to begin to heal, but wind slabs remain possible to trigger on Monday. Pay attention to how the snow looks and feels to help you anticipate which slopes and features harbor wind slabs. When you see a textured snow surface or find firm or hollow snow, expect wind slabs on similar aspects. Steer around wind-loaded terrain and seek out less wind-affected or lower-angled areas.

    (2/20/2021) Example: This human triggered wind slab avalanche occurred Saturday 2/20 in the Crystal backcountry. S, 6000' Pickhandle Pt. Photo: Jen Daniels.

  • Loose Wet

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

    Temperatures will rise across the region Monday and increase the likelihood for loose wet avalanche activity especially in areas that did not see loose wet activity on Sunday. The southern volcanos have the best chance for stronger sun, but regardless of where you are use clues such as rising temps, sunny skies, and water and snow shedding from trees as your first clue that loose wet avalanches may be following. While we expect these slides to remain isolated to very steep slopes, they could entrain snow and grow larger. If you see these clues, choose lower-angle terrain and shadier slopes.

    (2/24/2020) Example: Rollerballs like these are a great indication that the snow surface is becoming wet and unstable. They can be the precursor to loose wet avalanches. When you see new rollerballs, steer away from similar slopes.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    3

    With several observed deep slabs near the Crystal BC releasing over the weekend we know the deep slab problem lingers. It may be difficult for a human to trigger one of these, but with rising temps on Monday, large fresh cornices failing, might have the oomph to do it. The high level of uncertainty and disastrous consequences surrounding this problem should factor into the terrain you choose. Consider limiting your exposure to any large avalanche path even those that start far above where you intend to travel. Many recent slides have run to the bottom of their runouts and even broked mature trees.

    (2/27/2021) This very large and destructive deep persistent slab was reported by multiple parties on Saturday 2/27. While we don't know exactly when it occurred, it is very recent. E, 6300' 6-8' deep. Union Creek HS-N-D3-R4-O Photo: Joe Hoch

Avalanche Discussion

In addition to the potential weak layers listed below, cornices grew very large and overhung during this stormy period. Give these giants a healthy amount of space. This includes staying out from under slopes where they loom above. Temps are rising Monday and natural and human-triggered cornice failures will become increasingly likely. Any cornice failure is likely to trigger a wind slab and may be able to trigger a destructive deep slab avalanche. 

Most locations around the West South receive 1-2’ of snow since Feb 25th. This adds to the jaw-dropping totals for the month of February. This recent storm combined with very strong winds shaped the snow surface in many areas. Very active weather periods like this need time for the snowpack to adjust. Don’t let the lull in the weather short-cut your decision-making process. 

While we continue to focus on the new snow, several layers exist in the snowpack that are worth mentioning. 

  1. 2/25: At the base of the most recent snow this interface may contain surface hoar, graupel, or a thin crust depending on aspect and location. If avalanches fail at this layer they may trigger easily and propagate widely. 
  2. 2/23: The frim crust formed during the atmospheric river may extend up to roughly 5800’. This snowpack marker can serve as a way to delineate recent storms. 
  3. Mid-January: The facet-crust layer from mid-January continues to lurk 5-8’ deep in the snowpack. The last avalanches occurred on this layer Monday at Crystal Mountain and likely in the Goat Rocks Wilderness. Very little information is known about the current condition of this layer or its grains. 

 

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