Bollettino valanghe

Tetons

Bridger-Teton Avalanche Center
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Pericolo valanghe

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

It remains possible to trigger a large avalanche on steep, exposed wind-affected slopes at upper elevations. Weak snow near the base of the snowpack is more easily impacted in areas with a thin snowpack or by large triggers like falling cornices. Loose snow sluffing is possible in steep terrain. Identify cornices looming above steep slopes as you travel and watch for cracking and drifting in upper-elevation terrain.

Problemi valanghivi

  • Wind Slabs

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

    New wind slabs up to 18 inches thick have formed at upper elevations over the last couple of days in exposed, wind-affected terrain. In Isolated areas, these slabs may be hiding evidence of older wind slabs. Wind slabs will continue to grow with recent snow and gusty winds up to 30 mph. Watch for wind transport, drifting, and stiff wind-affected areas around exposed terrain. Watch for shooting cracks coming from your skis. If you find any of these red flags, move to more sheltered terrain.

    Watch for dry loose sluffing on steep terrain in sheltered middle and upper elevation terrain. Sluffing could be fast-moving where loose snow exists on melt-freeze crusts from last week.

    Cornices have grown large. Minimize time spent on slopes with cornices looming overhead. Cornices can break unexpectedly and tend to crack further back along the ridge than you might expect. Warming temperatures increase the likelihood of cornice failures. Cornice falls act as very large triggers and are the most likely way to trigger a deep persistent slab avalanche.

    (3/8/2024)

    Very large avalanche in wind-affected terrain likely triggered by a cornice fall on the westside of the Tetons.

  • Deep Persistent Slabs

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

    The deep persistent slab problem exists on all aspects at upper elevations and west through north through east aspects at middle elevations. Weak snow from December is buried up to 5+ feet. This weak snow is sitting under a stiff slab and is stubborn to human triggers. Cornices are the most likely way to trigger an avalanche. This is a low-likelihood and high-consequence problem, meaning the chances of triggering an avalanche on this weak layer are low but if triggered, it will be a large and destructive avalanche. Watch for cornices as you travel and evaluate thin, steep rocky, and wind-affected areas carefully.

    (3/6/2024) Crown of a very large (D3) avalanche in the South Fork Teton Canyon. This slide was triggered by a cornice fall on the right side of the photo. The avalanche occurred in steep, rocky NE-facing terrain at 9400' and ran 2400' to the valley floor and broke many mature trees.

    Photo: Cameron Galt

Avalanche Discussion

   

Thoughts on the Deep Persistent Slab Problem

While this is not the only avalanche problem we face, it deserves some discussion. We have transitioned the persistent slab problem to a deep persistent slab problem this week due to the average depth of the weak layers and the stubborn nature of this problem. We have not had a human-triggered avalanche fail on these weak layers in quite some time. However, we have had very large avalanches resulting from cornice falls or possibly heavy wind loading (large trigger) in the last week and a half. 

There are 2 situations where the deep slab hazard is elevated that should be on your radar as you travel, and when combined, caution is warranted:

  • Thin areas in the snowpack. The Teton snowpack is deep right now which works in our favor. However, shallow areas remain the most likely place to trigger deep weak layers. Steep, rocky, and wind-affected slopes should be evaluated carefully due to a higher likelihood of impacting weak layers closer to the surface. This is especially true on the north half of the compass at middle and upper elevations. Unsupported slopes above cliffs should be considered suspect. If identifiable, slab margins (edges of start zones for example) are also generally thinner. Probing areas of concern gives you depth information.
  • Large Triggers. Cornices remain a concern and are the most likely trigger for a deep slab avalanche. We are in for a warm-up starting tomorrow and into the weekend. Warming temperatures make cornices and slabs more sensitive. Steer clear of steep slopes with looming cornices. Rapid loading is of less concern right now with high pressure moving in this week but should be on the radar if the weather changes and we get a forecast for large amounts of precipitation. This will further stress the snowpack.

The best way to manage this problem is to build in a large margin for error in your decision-making around avalanche terrain. This includes traveling where the snowpack is deepest, identifying the presence/depth of the weak layer (probing or digging), and avoiding thin, steep, rocky, and wind-affected areas. This problem can be hard to identify and will not have signs of instability. Tracks on a slope may indicate increased stability but they are not conclusive evidence. When in doubt, or if uncertainty is high, choose more conservative terrain.

Regioni coperte