Bollettino valanghe

Tetons

Bridger-Teton Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Triggering an avalanche 1-2 feet deep in recently drifted new snow in steep terrain is likely.  Deeper weak layers remain buried and are closest to the surface on thin, rocky wind-affected slopes. Use cautious route-finding and conservative decisions around steep, exposed terrain where surface snow instabilities exist.

Problemi valanghivi

  • Wind Slabs

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

    Soft wind slabs up to 2 feet deep can be found at upper elevations along ridges and exposed terrain. Wind-affected snow may still be found at middle elevations but only in isolated, very exposed areas. New snow may have buried older, hard wind slabs. Watch for pillows, drifts and areas of stiffer snow as you travel. Soft slabs built by gusty winds will most likely break at your feet. If you observe cracking or collapsing, seek out sheltered terrain. Small wind slabs can easily knock you off your feet in consequential terrain.

    Dry Loose: In steep terrain that has not been wind-affected, watch for sluffing. Monitor the depth and cohesion of surface snow and use small steep test slopes to gauge how much snow can be entrained in sluffing. Be mindful of this problem around trees and cliffs where small amounts of entrained snow can easily push you over.

    (2/24/2024)

    A wind slab that caught and carried a skier 500 feet in Grand Teton National Park.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1.5–2.5

    The persistent slab problem exists at middle and upper elevations and is more prevalent on the north half of the compass. Steep, rocky, unsupported and wind-affected terrain on west through north through east aspects should warrant extra caution. Weak snow from earlier in the winter is buried 3 to 5 feet under a hard slab. You will likely not get any feedback or see any clues of this problem as you are traveling. Digging and probing are effective ways to locate the depth and distribution of weak sugary snow. Any avalanche failing on these deep layers will be large and destructive. While triggering is unlikely, continue to be mindful of thin areas in the snowpack. 

    Cornices continue to grow.Minimize time spent on slopes with cornices looming overhead. Cornices can break unexpectedly and can crack further back than you expect along ridgelines. A large cornice falling into a persistent slab problem will act as a large trigger and possibly trigger a large avalanche. Give cornices a wide berth.

     

     

    (2/17/2024) Photo: Teton County SAR

    A very large persistent slab avalanche that occurred on No Name Peak after a period of significant loading.

Avalanche Discussion

There are 4 distinct avalanche problems mentioned above - persistent slab, wind slab, dry loose, and cornices. The dry loose is lumped in with the wind slab because it has similar distribution. Cornices are mentioned in the persistent slab problem because cornices can act as large triggers and impact deep weak layers when they fail. As I travel through avalanche terrain, my decisions are based on managing the current risk. What avalanche problem is going to get me? Where is it located? and How bad will the consequences be if I get caught? The answers to these questions are located in the graphics at the top of each problem description. The most likely problem to get me right now stems from surface snow instability. We have had multiple observations recently of people kicking off wind slabs - especially at the exposed top of couloirs and other confined terrain features. One person was caught and carried 500 feet. This problem is easily avoidable by choosing to not enter steep wind-affected terrain. What is not addressed in the avalanche problem graphics is the consequence of a small avalanche knocking you off your feet and sending you down a couloir or over a cliff. That hazard is for you to identify and mitigate. Can you manage the wind slab (hazard) with a ski cut (mitigation)? The answer to that question has a lot of uncertainty depending on how large and hard that slab is. Wherever there is uncertainty combined with a potential consequence of injury or worse, increase your safety margin by choosing safer terrain (less steep and without wind-affect). Keep that in mind as travel.

Thanks for sending in your observations! It is tremendously helpful to paint a more accurate picture of the hazards out there!

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