Bulletin d’avalanche

Banner Summit

Sawtooth Avalanche Center
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Danger d’avalanche

Sat
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

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 the sun stays out longer than expected this morning. If you're sinking into a mushy snowpack, stick to gentler slopes or find cooler snow to ride.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Multiple slab avalanches were reported following Tuesday's storm. They failed on weak snow that developed at the surface during the drought of January and early February. Check out Chris' video (at right and below) for an idea of what we're dealing with. 

    The majority of these slabs occurred 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 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 are not your more predictable, run-of-the-mill wind slabs. You can't simply look for and avoid areas of wind-drifted snow. These avalanches are likely to behave in ways that surprise you. They can wrap around terrain features like ridges and may be triggered from flatter terrain below, above, and to the sides of steep slopes. 

    ADDITIONAL DISCUSSIONCloud cover and cooler air will reduce the chance of wet snow avalanches. That said, the snowpack will take a bit of time to solidify after days resembling a bowl of oatmeal. If the sun peaks through the clouds, it won't take long to break down any surface crusts that formed last night. If you're sinking into slush, find gentler terrain or cooler slopes to ride.

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 8-10" 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. Wednesday 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. 

Wednesday, 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.

Régions couvertes