Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Fri
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Sotto il limite
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In sintesi

You're most likely to trigger a large avalanche on shady (NW-N-NE-E facing) upper and middle elevation terrain. These slides could be triggered remotely—from flatter terrain below, above, and to the sides of steep slopes. Wet snow avalanches are possible. If you're sinking into a mushy snowpack, stick to gentler slopes and don't linger under large, steep, rocky terrain.

Problemi valanghivi

  • Persistent Slabs

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

    Ben observed natural slab avalanches near Bull Trout Point (observation, photos to the right and below). These slabs likely failed on weak snow that developed at the surface during the drought of January and early February.

    The majority of these slabs failed on shadier aspects between 8,000 and 8,500'. This band seems to have the ideal combination of slab formation and a well-preserved weak layer. Why? It's stayed mostly dry; high enough to escape much of the rain, and shaded enough to avoid melting in the sun. It's protected. This band is near the upper/middle elevation transition, so it's just low enough to avoid being heavily weathered by the wind. 

    These avalanches are likely to behave in ways that surprise you. They can wrap around terrain features like ridges and may be triggered remotely—from flatter terrain below, above, and to the sides of steep slopes. These are not your more predictable, run-of-the-mill wind slabs. Simply looking for and avoiding areas of wind-drifted snow is not enough. Let's all take a big, collective step back as we learn more about how this problem will behave. 

    ADDITIONAL DISCUSSIONKeep your eyes peeled for wind slabs at upper elevations. Expect to encounter stiff drifts near ridgelines, in chutes and couloirs, and on aprons below gullies. Think about the consequences of triggering a small wind slab avalanche before committing to serious, consequential terrain. 

    (3/1/2022) These slab avalanches failed on N/NE facing slopes at 8,300-8,500' near Banner Summit. Based on their location and the appearance of the crowns they likely failed on a layer of weak snow underneath. You can see that the bed surface has a grey/dark appearance to it, which is generally an indicator of faceted grains. 

  • Loose Wet

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

    We've observed countless wet loose avalanches in the last couple of days. Most of these occurred at middle and lower elevations during bouts of rain on Tuesday. Yesterday in the Sawtooths, I watched as the sun triggered small avalanches on very steep, rocky, upper elevation slopes. Rain and yesterday's sun released most of the "easy pickings".  I'd expect less natural avalanche activity today, but very warm temperatures and periods of hot sun will keep this problem on the table. 

    Last night was the third night with a weak or nonexistent overnight freeze. It won't take long for thin surface crusts to break down and under them, it's still a soupy mess. Today, avalanches are most likely at low elevations and on very steep slopes that face the sun. Most of these slides begin near rocks or where the snowpack is less than about 2' thick. 

    If you're sinking into slush, it's time to find gentler terrain or cooler slopes to ride. Although I'd expect most of these slides to be relatively small, it's not a good day to linger under steep slopes. Avoid low elevation terrain traps, like creek/river bottoms and gullies, especially in the afternoon. 

    (3/1/2022) These wet loose avalanches failed near Banner Summit on a N-facing slope at 8,200'. They likely failed during the day on 3/1, as the rain line climbed when rain was falling on new snow.

Avalanche Discussion

Weak snow developed at the surface during the drought of January and February. Small storms clipped the northern end of the forecast area, favoring the Banner Summit Zone. Tuesday's storm brought an additional 7-10" of dense snow to Banner Summit above about 8,000' capping off a slab that's anywhere from 1-1.5' thick. This last storm proved to be just enough to tip the scales, producing multiple slab avalanches near Bull Trout Point (observation). 

South of Banner is a different story. It's snowed less, and the slab is thinner. Only a handful of slab avalanches were observed in the Sawtooths, most of which were small wind slabs (photo). This doesn't mean the weak layer in these zones is absent. Yesterday in the northern Boulders, Chris found unstable snowpack test scores, and observed cracking in ~1' drifts (observation). These drifts sat on the similar weak layers that formed during the drought. The difference here, as well as other areas outside of Banner Summit, is that these conditions are more infrequent and require some wind-loading to build the slab. 

Yesterday, I spotted this large persistent slab avalanche on the N. face of Saviers Pk in the Smoky Mountains. While an apparent outlier, it's an indication that this problem lurks in isolated areas with ideal wind-loading and a well-preserved weak layer. You're not likely to find many locations that can produce this large of a slide, but the possibility is there. This avalanche and the ones near Banner Summit may foreshadow what's to come if large-scale snow returns to the forecast area.

Regioni coperte