Bollettino valanghe

Tetons

Bridger-Teton Avalanche Center
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Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Winds over the past week have blown the recent snowfall into slabs and drifts in upper elevation and alpine terrain. Avoid steep slopes where you find wind-drifted or pillowed snow, and areas where the wind has drifted new snowfall onto crusts. Triggering an avalanche on weak layers buried 3+ feet deep remains a possibility on very steep, rocky, wind-affected slopes at middle and upper elevations.

Problemi valanghivi

  • Wind Slabs

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

    The combination of new snowfall and high winds from the previous 48 hours has created wind slabs on ridges and other exposed terrain features. Though periods of higher winds have finally ceased, we'll continue to deal with the aftermath for a few more days. These strong winds produced a number of small to medium-sized natural and triggered wind slab avalanches across the forecast area. Fortunately, these wind slabs will be easy to identify. Watch for snow that is denser than snow found on wind-sheltered slopes and tell-tale clues such as surface texture and a pillowed, drifted appearance. These will be less sensitive today, but I'd still avoid steep slopes where you find these indications of recent wind loading.

    New snow will remain more sensitive where it has fallen on a crust on the southern half of the compass. Lingering weak snow also exists deeper in the snowpack, and wind-drifted areas pose a higher hazard for triggering a larger avalanche on one of these layers. 

    (2/6/2023)

    Two separate parties were involved in avalanches in an exposed area outside JHMR yesterday. This illustrates the importance not only of group communication and preparedness but also choosing terrain that is appropriate for a given hazard (Ralph's Slide observation).

  • Persistent Slabs

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

    This zone has persistent weak layers buried 3 to more than 5 feet deep on most middle and upper elevation slopes. On the western side of the Tetons yesterday, I found a shallow snowpack and a thick layer of facets from the January 26 storm. Though my pit did not propagate, I suspect an area with a heftier slab would, and finding this structure alone brings pause, and I suspect it will stay with us for a while. The presence of these layers is the most important observation. 

    Deep Persistent Slab: Areas on the southern half of the compass in the middle and upper elevations harbor deeply buried weak snow from late November. I don't even bother to do a snowpack test where I know this exists because 1) they don't work well on layers this deep, and 2) the presence of these layers is the most important observation. With deeply buried weak layers, it's important to avoid thinner areas where you can more easily impact the weak layer. You can reduce your risk of triggering any and all of the above avalanche problems by avoiding: 

    • Wind-affected terrain: The wind can create thinner spots where the weak layer is closer to the surface. These are often connected to wind-loaded areas where there is more load on the weak layers.
    • Steep, rocky slopes: Rocky or "alpine-like" terrain typically has shallow areas where your weight can more easily affect buried weak layers.

Avalanche Discussion

State of the Snowpack

The Togwotee snowpack is the shallowest and weakest, especially around the Grouse and Brooks areas. As is not uncommon in this area, there is plenty of weak, faceted snow—what's lacking is a slab of cohesive snow atop it in many spots. Currently, unstable slopes are largely limited to where recent and/or past wind events have created dense or stiff snow in the upper pack. The incoming storm tomorrow will favor the Tetons and Togwotee, so expect to see changing conditions and higher wind speeds.

The Greys River zone is the unpredictable one in the middle. There is a great deal of variability across this zone, but it all falls somewhere between the two scenarios described above. The thin, windswept snowpack of the Salts has characteristics of Togwotee, where wind slabs sitting atop weak, faceted snow are the main concern. The Wyoming and Snake River areas have a bit deeper snowpack, with early-season weak layers buried 2-4 feet deep. In the Salt Range, the faceted snow near the ground seems especially pronounced.

The deepest snowpack exists in the Tetons*. I put an asterisk here because the west and east side of the range have entirely different snowpacks, and the west side remains far thinner with a more obvious weak layer development that will persist. Overall, a sandwich of persistent weak layers remains highlighted on the southern half of the compass in the middle and upper elevations. My primary concern is a thicker layer of facets exhibiting a more widespread pattern which was buried in late January. These layers are buried 3+ feet deep due to the nature of the larger storm that buried them. This, to me, reads that triggering an avalanche on them may be more difficult, but likely larger and very consequential. This layer is worth looking for in pits and assessing carefully with recent and changing weather on the way. Avoiding thinner "trigger points" is the name of the game—these are more likely to be found in very steep, rocky, alpine terrain that is prevalent on the west side, but less so on the east.

So there you have it— familiarize yourself with the snowpack in areas you frequent, keep your head on a swivel with incoming weather, know the people you like to get out with and how well you all communicate—and choose terrain that fits your assessment of all of the above. 

 

 

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