Bollettino valanghe

Salt River and Wyoming Ranges

Bridger-Teton Avalanche Center
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Pericolo valanghe

Sun
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Human triggered avalanches are possible at the middle and upper elevations today, especially where recent snow has drifted into stiff slabs of snow that overlie buried weak layers. Steep, rocky, wind affected, and shallow areas are the most likely zones to trigger slabs. Monitor the influence of the sun today and minimize exposure times on steep sunlit slopes. You can use tools such as probes and shovels to determine whether or not buried weak layers exist on the slopes you plan to ski or ride. 

Problemi valanghivi

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    Buried persistent weak layers exist within the snowpack. On windward slopes these layers are within 2-3 feet of the snow surface. On leeward slopes these buried weak layers could be in excess of 5 feet deep.

    Use you shovel and probe to determine if buried weak layers exists. Pay attention to signs of instability such as audible collapsing of the snowpack.

    (1/5/2023)

    This avalanche was triggered by a rider at Jack Hollow on a southeast aspect at 9,500 feet.  It failed on weak snow in the lower half of the snowpack and was approx. 3 feet thick. 

    Photo: Antonioli

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Variable winds over the last 24 hours have created wind slabs at the upper elevations that are 1-2 feet deep. Slabs could be both soft and hard. Northerly and westerly winds are forecasted for today, causing abnormal loading patterns.

    Monitor the wind direction and pay attention to signs of instability such as cracking within wind drifted snow.

    (1/19/2023) Cornice at summit, this photo is looking NW.

Avalanche Discussion

Transition to Deep Slab Instability: Forecasters at the BTAC have chosen to categorize the current persistent weak layer problem as a Deep Persistent Slab Problem as defined by the Conceptual Model of Avalanche Hazard (Statham et al, 2017). Characteristics of a Deep Persistent Slab include periods of activity followed by periods of dormancy, structure that is conducive to failure initiation and crack propagation, and incremental building of the overlying slab over many storm cycles. While there are no definite depth restrictions of a Deep Persistent Slab, previous research has looked at events with minimum crown depths ranging from 0.8 to 1.2 meters (Conlan and Jamieson, 2016; Conlan et al., 2014; Marienthal et al., 2015; Savage, 2006).

Forecasters at Bridger Teton Avalanche Center feel that the aforementioned characteristics more accurately describe the current snowpack setup (highlighted by weak basal structure) than a standard persistent weak layer.  

The southern ranges have picked up a fair amount of low density snow over the last week. Winds have been light but the new snow is readily available for transport. You are most likely to trigger an avalanche where wind slabs lie on top of buried weak layers in steep, shallow, and rocky areas.

 Natural avalanches have been limited to new snow instabilities and wind slabs over the last week. 

Current snow surfaces are made up of low density stellars and near surface facets in many locations. Buried persistent weak layers from late November and early December are buried over 1.5 meters deep on leeward aspects. On wind exposed aspects these layers are much closer to the surface and are reacting in the moderate to hard range in stability tests. 

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