Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

The combination of new snow, wind, and buried weak layers will make human triggered avalanches possible today. Cracking within wind drifted snow and collapsing of the snowpack are warning signs of heightened avalanche conditions. Steep, rocky terrain that has been wind affected should be evaluated carefully.  

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Thin wind slabs developed above 9k' yesterday on NW-SE aspects. These slabs were anywhere from 4 to 8 inches thick around 9.5k'. Winds calmed overnight and temperatures are in the single digits at the upper elevations. Winds are forecasted to be in the 20-30 mph range this afternoon with little to no new snow and temperatures around 20 degrees F. Slab depths could reach 1 ft at the upper elevations and will likely be stubborn.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2.5

    The November 27th Layer is now buried 2-4 feet down from the surface of the snow at the middle and upper elevations. At the lower elevations this layer is 1-2 feet down on all but Southerly aspects. Human triggered avalanches remain possible, especially at the middle and lower elevations where it is closer to the surface. Field observations are consistently finding unstable conditions in snowpits, with failure and full propagation continuing to occur several days after new snowfall. New snowfall and wind will add stress to this layer, although natural avalanches remain unlikely today. 

    Have removed persistent slab problem from the lower elevation band not for a lack of a continuous weak layer, but for a lack of a continuous slab. This situation will change with the next significant snowfall at the lower elevations. 

Avalanche Discussion

Yesterday the Tetons picked of 2-4 inches of snow in a short wave trough. Ridgetop winds averaged around 20 mph out of the SW and thin wind slabs (4-8" thick) developed at the upper elevations. No significant avalanches were reported. Cloudy and breezy conditions are expected today with minimal snowfall. 

The Teton Trickle throughout the week left the range covered with about a foot of low density snow. This snow received a zipper crust on Southerly aspects on December 7 which should limit the available snow for transport. The November 27 layer (mid November dry spell) is now buried 2-4 feet below the surface of the snow. This layer is composed of crust facet combinations on S, E, and W aspects. On Northerly aspects this layer is made up of near surface facets and even some surface hoar in some locations. Field observations continue to reveal unstable test results with this layer in snowpits. Lower elevations have the poorest structure but generally lack slab qualities that are favorable for avalanches (exceptions abound).

So far Triple Dip La Nina conditions are treating the Tetons favorably. Current snow water equivalent measurements show Grand Targhee to be 114% of median value while Phillips Bench sits at 130% of median. The Togwotee Pass snotel is at 95% of median and Willow Creek in the Salt River Range is 135% of median. 

Regions covered