Bollettino valanghe

Salt River and Wyoming Ranges

Bridger-Teton Avalanche Center
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Pericolo valanghe

Fri
Alta quota
1 · Debole
Limite del bosco
1 · Debole
Sotto il limite
Senza grado
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In sintesi

Triggering a slab avalanche up to 3 feet thick is unlikely but not impossible today.  Watch out for unstable snow in isolated areas of steep, rocky terrain that may have been wind-affected. Low avalanche danger does not mean that there is no avalanche danger.

Problemi valanghivi

  • Persistent Slabs

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

    Weak layers of snow that fell in November and are buried 1-3 feet below the surface continue to show the potential for cracking and collapsing in snow pits. An avalanche capable of injuring of burying a person was triggered by snowmachiners last Saturday on a steep and shady slope at 9,800 feet near Gunsight Pass. The avalanche was up to three feet thick and is an example of an isolated terrain feature that's capable of producing an avalanche. In this case, the slope failed on the second pass on the slope in a wind-drifted area. Wind-affected and rocky terrain on steep, shady slopes increase the odds that you might encounter a thin spot under a slab of unstable snow. Continue to assess the surface to look for signs of wind-loading or scouring on the aspects depicted above and consider the consequences if caught in an avalanche.

    These surface clues and the weak layers beneath will be obscured and stressed by new snow that arrives later today and continues, hopefully, through next week.

    A north facing slope near 10,000 feet with a start zone in wind-affected snow.

    (12/30/2023) Photo: Shane Copeland

Avalanche Discussion

There has been very little avalanche activity since early December in western Wyoming. The exception to this occurred during and just after the new snow and north wind that arrived right before Christmas. That storm brought some natural and human triggered avalanches before another ten day stretch with few, if any signs of instability until the avalanche referenced above on December 30th. Despite this stretch of relatively stable conditions, maintain good, safe travel practices and hedge your bets against a rare but potentially deadly avalanche, especially above terrain traps. Also, bear in mind that the snowpack remains thin with many obstacles just below the surface most everywhere and with very thin coverage at low elevations and steep, south facing terrain.

The most recent dry spell has transformed the top 6 to 8 inches of our snowpack on shady aspects into soft, cohesionless facets (recycled powder), in most places over a firm slab.  Steep aspects facing the sun have crusts and a much thinner snowpack due to the many days of sunshine and relatively warm temperatures.  There is also widespread surface hoar which is a particularly sensitive weak layer when buried. These surface conditions and buried weak layers will, no doubt, produce avalanches when new snow arrives in any significant amount over the upcoming period of stormy weather.  A variety of challenges will emerge due to the very poor snowpack stucture on northerly aspects, as well as the more recently formed, weak, recrystallized snow at or near the surface. The snowpack configuration and weather pattern is not typical in this area known for a deep snowpack with steady snowfall. As such, knowing exactly when and how large avalanches will occur is a subject of much speculation, without clear and obvious answers. One thing that is certain is the poor snowpack structure will produce avalanches and make for dangerous conditions in the mountains. More on that topic later following this final day of relatively benign condtions.

The number of quality observations this season has been very helpful for the forecast team and the community at large. Many thanks to those of you who have generously shared your time and this invaluable information!

 

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