Bulletin d’avalanche

Tetons

Bridger-Teton Avalanche Center
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Danger d’avalanche

Fri
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Weak layers of snow are buried beneath slabs up to 3 feet thick. Human-triggered avalanches remain possible on many aspects and elevations. The middle elevations, particularly around 7,500 to 8,500 feet, have a more continuous weak snow layer. Due to the unpredictable nature and locations of these persistent weak layers, your best defense against triggering an avalanche is to play on lower angled slopes.

Problèmes avalancheux

  • Persistent Slabs

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

    Areas of faceted snow, crusts combined with facets, and buried surface hoar are widespread across all forecast zones but are concentrated in low to middle elevations. Field observations are consistently finding unstable conditions in snowpits, with failure and full propagation continuing to occur several days after new snowfall. Even more important, remote triggering was observed yesterday just south of the Tetons in the Snake River Range. Evaluate the snow in your pits to see if there is a weak layer below and a slab above. This recipe can crack a long distance and fail above or well beside you. Lower elevations have less snow and less slab over these weak layers thus the lower rating. Remember that low avalanche danger does NOT mean no avalanche danger, merely that avalanches are unlikely and probably small.

    (12/7/2022)

    BTAC forecaster triggered this avalanche while tracking down unstable snow in the Snake River Range.

    Photo: Gabriella Antonioli

Avalanche Discussion

Nearly every snowpit in the observations over the past several weeks has continued to propagate at the middle and upper elevation bands (around 7,500 to 10,000 feet). These areas include well traveled areas like Glory Bowl and the sidecountry terrain of Jackson Hole Mountain Resort. The results of avalanche mitigation on closed runs at Snow King on Tuesday, continued collapsing in the snowpack and a remotely triggered avalanche should serve as bullseye information.  These recent events are a good reminder that this  snowpack is extremely variable across the terrain with a level of complexity that makes assessment challenging. There is no doubt that luck has been playing a more important role than it should in the lack of human involvment in avalanches in recent days. 

The weak layers in the snowpack are persisting predominantly in the middle to lower elevations, dependent on the mountain range.  These pits are failing on a variety of weak layers found on both southerly and northerly aspects, and primarily hold a mix of thicker layers of small facets, and/or surface hoar.  A common theme appears to be high strength in extended column tests (high # of taps before failure) and fair structure (not the worst, not the best).  The slab above these weak layers can be significant and thick in some places which may make them harder to trigger, but it is possible to find thinner spots in our developing snowpack where you can trigger this layer. Low probability but high consequence scenarios like these are difficult to plan for and navigate around, leaving the aforementioned luck playing an outsized role in safe travel in the terrain.

Warm temperatures and sunshine impacted solar aspects yesterday and likely degraded quality of skiing conditions. You may find a thin crust in some locations.

 

Régions couvertes