Lawinenlagebericht

Tetons

Bridger-Teton Avalanche Center
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Lawinengefahr

Thu
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

Avalanche danger will rise to Considerable this afternoon as natural avalanches become possible on sunny, wind sheltered slopes. Wet, slushy snow surfaces indicate that water is seeping into the snowpack which may trigger a slab avalanche up to two feet thick.  Look for soft snow that isn't saturated for better turns and less danger. Terrain near or under cornices should be given a wide buffer.

Lawinenprobleme

  • Wet Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Likely
    Größe
    1–2

    After several warm days and cool nights, water appears to be reaching weak layers and crusts in the upper snowpack. Two avalanches were triggered yesterday afternoon, one remotely by a forecaster south of Teton Pass in a sunny, wind protected bowl and one triggered by a snowcat pushing snow onto a sun-baked slope at JHMR (see photo).

    Recent avalanche activity prior to these two slides was limited to wet loose sluffs, a few of which were large and potentially dangerous. Those occurred primarily on the first warm day last week (Thursday and Friday) when sun heated up fresh snow. Since that time, every day seemed to be a replay of the previous one, with sunlit surfaces becoming wet 3-4" down but no reported wet sluffs or slabs. Recent snowpits are now showing water pooling on crusts at various depths beneath layers of dry snow. Assessing the exact location and depth of these crusts prior to skiing a slope isn't really feasible due to the spatial variability of the layers, but observing the warm temps, calm winds and slush on the surface is easy. Monitor the snow surface as the day heats up. Surface crusts formed overnight melt quickly in areas that experienced a light freeze and will send more water into the snowpack. Think twice if you are sinking in past your ankles and be mindful of potentially forceful, wet loose avalanches, even on less sunbaked slopes.

    (3/19/2024) This avalanche was triggered by a snowcat pushing snow onto a ski slope yesterday afternoon. 

  • Deep Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely
    Größe
    2–3

    Hard slabs 3-5 feet thick overlay weak snow that formed earlier in the season. Shallow, rocky, and unsupported terrain on the north half of the compass is where this problem has been most active. Thin areas in the snowpack can act as trigger points and are most common in these locations. It is currently unlikely that a human would trigger one of these slabs. Larger triggers, like cornice fall or surface snow avalanches, still have the potential to impact weak layers buried deeply in the snowpack and initiate a much larger avalanche.

    Cornice Fall: Cornices have grown large and failures are possible, especially during the heat of the day. Give cornices a wide margin and avoid lingering under heavily corniced ridgelines. Right now, cornice falls are the most likely way to trigger a very large persistent slab avalanche.

    (3/5/2024)

    Very large persistent slab avalanche that failed during the early March storm cycle. This terrain characterizes where this problem is most active. Very steep, unsupported slopes near cliffs. Also note the large cornices and potential trigger. 

    Photo: Dan Hays

Avalanche Discussion

The two avalanches yesterday are good evidence that water continues to flow deeper into the snowpack despite cold temperatures at night. This daily flow creates more pore spaces with less resistance to water, allowing water to flow deeper into the snowpack, lubricating crusts and melting weak layers there. The timing of this action is challenging to nail down accurately but these two slides could very well be a precursor to a more reactive avalanche problem today. The wind speed may exceed those forecasted and bring the trend to a halt. Only time will tell. Good turns can be found in dry snow that remains on shady, northerly elevations above about 8,000 feet and great corn skiing can be found with the right timing and route-finding. 

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