Avalanche forecast

Tetons

Bridger-Teton Avalanche Center
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Avalanche danger

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

The combination of recent snow, wind, and buried weak layers make human triggered avalanches possible today. Cracking within wind drifted snow and audible collapsing of the snowpack are signs of instability. Carefully assess the snowpack before entering steep, rocky terrain with thin coverage.  

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    The November 27 layer is now buried 1-3 feet below the surface of the snow at the middle and upper elevations. This layer is present on all aspects at these elevations with varying degrees of weakness. Southern aspects above 7500', and Northern and Eastern aspects at the middle elevations seem to be the worst, but as stated earlier the problem is widespread. Shallow areas of the snowpack in and around rocky zones are also slightly suspect, especially where recent low density snow and light/moderate winds have conspired to increase loading. 

    Stability is trending upward as cold temperatures and incremental loading are working to decrease the reactivity of the layer. Test scores are going up in snowpits and avalanches on this layer seem to be few and far between. The possibility of size 2 avalanches keeps the danger at Moderate, but we will see in the coming days if this layer becomes truly "unreactive".

    (12/11/2022) Wind slab on Mt. Oliver (possible persistent).

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Thin wind slabs at the upper elevations are possible. Light, continuous snowfall over the last several days and NW winds during yesterday afternoon and last night could combine to form slabs on top of crusts on southern aspects. Slab depths of 6-12" are possible in leeward terrain, but cold temperatures should help with reactivity. Raymer has picked up 6 inches of low density snow over the last 4 days and Rendezvous Summit has recieved 530 total miles of wind out of the NW in the last 24 hrs. Wind slabs could be more prevalent on the west side of the range over by Targhee where NNW flow is impinging on the range. 

    (12/14/2022)

    Isolated areas of wind slab could be found in upper elevations following the low density snowfall in the 13/14th.

    Photo: Frank Carus

Avalanche Discussion

Yesterday and last night the Tetons picked up a trace to one inch of snow (5% blower). Gusty winds out of the NW were prevalent yesterday afternoon and last night, primarily at the upper elevations. 

Stability concerning the persistent weak layer from November 27th seems to be on an upward trend throughout the range. ECT and PST scores are going up, and avalanches on this layer have been few and far between. The two storm systems from November 27- December 3 created a nice hard slab on top of the weak layer but above those layers the pack is mostly right side up with low density snow on top (where it is not wind-affected). This does not seem to be the best density profile for a slab to propagate a fracture and the cold temperatures aren't helping either. 

Hemmed and hawed about dropping the danger rating at the mid elevations to low. After some grappling with the Conceptual Model of Avalanche Hazard (Statham et al.,2017) a danger rating of Moderate was decided on for the time being. With slab depths in the 1-3 foot range, size 2 avalanches are totally within the realm of possibility in steep avalanche terrain at the middle elevations. The issue then comes down to sensitivity to triggers. Is the November 27 layer "stubborn" or "unreactive"? Would a well placed bag of ammonium nitrate fuel oil (ANFO) produce an avalanche in certain locations right now? Possibly. Depends on the slab characteristics. So certainly stubborn but maybe not unreactive quite yet.

Snow depths generally range from 3-6 feet above 9k’ in the Tetons. The Beaver Creek snow stake (6600’) is currently reading 30 inches. Height of snow (HS) values for Surprise Meadows and Rendevous Bowl are 60 inches and 51 inches respectively, with total snow values of 138 inches and 186 inches respectively. On the west side of the Tetons the Chief Joseph site sits at a depth of 60 inches with a year to date total of 149 inches. As far as snow water equivalent goes the Tetons are currently sitting at above average values. Targhee Snotel (9260’) is at 106% of median, while Phillips Bench (8200’) and Grassy Lake (7265’) are at 120% and 112% respectively.

  

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