Bollettino valanghe

Tetons

Bridger-Teton Avalanche Center
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In sintesi

Avalanches could still be triggered on wind loaded upper elevation terrain from moderate winds drifting snow three days ago. Rapidly warming temperatures today above freezing will create unstable snow, especially on slopes facing the sun, by the afternoon. Use extra caution around and underneath terrain where large natural cornice falls are possible today. Cornice falls can trigger very large avalanches failing on buried weak layers. 

Problemi valanghivi

  • Wind Slabs

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

    Recent moderate wind formed wind drifted slabs 3 days ago that could still be sensitive to triggering an avalanche in the upper elevations. Winds were actively loading terrain ranging 20-30 mph from primarily the west and southwest. Slabs will be found on leeward and cross loaded terrain 1-2 feet and possibly 3 feet in isolated areas. Signs of instability could be less obvious than previous days, but still possible to trigger once you commit to a slope. Steep and confined features, such as couloirs, and ridgelines or similar terrain features should be assessed thoroughly for reactive slabs. 

    Cornice Falls: Warm temperatures today will increase the sensitivity of cornices. Give cornices a wide margin of safety and be careful along ridgelines as they can break further back than expected. Limit exposure under cornices, particularly in the afternoon. Cornice falls are the most likely way to trigger a very large persistent slab avalanche. Check out this observation highlighting recent Cornice Falls. 

    Deep wind slab avalanche on leeward terrain off a ridgline. This avalanche failed directly on a large pilllow/drift. 

    (3/7/2024) Photo: Colin Boeh

  • Loose Wet

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    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1

    Clear, sunny skies will decrease stability on southerly aspects by the afternoon. Watch for snow surfaces to become wet and easier to penetrate as a sign of wet loose avalanche potential. These avalanches will be small but could knock you off your feet or machine in steep terrain. The snow around rocks and cliffs will warm up earlier in the day resulting in more activity. Upper elevation wet loose potential will be isolated to southerly aspects around that steep, rocky terrain. 

  • Persistent Slabs

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

    Weak snow formed in December is persisting 3-5+ feet deep below hard slabs. These weak layers have been tested over the last week with 70” of snow and 7.5” of SWE since March 1st (Raymer weather station, JHMR). Numerous avalanches occurred during this storm cycle that failed on these weak layers, most likely from cornice falls (Treasuer Mountain). Large loading events and large triggers, such as cornice falls, have been able to produce very large avalanches on these layers. The impact of a rider triggering these layers is unlikely. Still the primary terrain that is most hazardous includes very steep, hanging snowfields above cliffs and rocky or notably shallow slopes. Keep in mind that a large wind slab release or cornice fall will make it possible to trigger one of these very large avalanches.

    (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

The last two days have felt like more typical days in March as the snowpack adjusts to a spring regime. There are a lot of stable slopes to travel on today. Use the information explained above to inform your terrain choice to avoid those specific areas where unstable snow and unpredictable cornice failure exists. Southerly aspects extending to the upper elevations have formed a stout melt freeze crust with strong solar influence and cold temperatures at night reaching the single digits. These large temperature fluctuations are slowly making recently formed wind slabs more stubborn to trigger. But warm temperatures above freezing will destabilize those wind loaded slopes by the afternoon. This is very relevant if traveling into the high peaks. Unstable snow was found in a higher elevation southerly aspect of the Nugget in GTNP yesterday. 

Rapid loading of snow with strong to moderate winds during the last storm cycle has increased the size of large cornices above 8500’ on N-NE-E-SE-S aspects. Multiple cornice falls were reported after the cycle as these cornices reached the tipping point of failure. Rapid warming tempeartures and strong solar influence today will destabilize cornices in the afternoon. Careful terrain choice will be necessary to avoid traveling beneath terrain where large cornices exist.  I also can't stress enough how notorious cornices are for breaking further back than expected while scoping terrain or looking for entrances to ride off ridgelines.  

We are absolutely heartbroken  to hear about the loss of two avalanche forecasters from Wallowa Avalanche Center and Northwest Avalanche Center over the last two days. Our most heartfelt condolences go out to their friends and family. The presence of these two will be truly missed in the mountains and community.

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