Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Mon
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Triggering a 1-3 foot thick avalanche is most likely on slopes with wind-drifted and stiffened snow at the surface. Although less likely, triggering avalanches is still possible on slopes sheltered from the wind. It also remains possible to trigger avalanches  remotely—from flat terrain below, above, and to the sides of steep slopes.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2

    You may be able to trigger slabs up to 3 feet thick on all aspects in mid and upper elevations. These persistent slabs are most likely to be triggered on wind-loaded slopes but are also possible in areas sheltered from the wind.

    Firm snow under your sled or feet and visual clues like rippled or dome-like surface textures are clear signs of wind slabs. Noticing firmer snow over softer snow with pole probing or poking around in a sled trench is another great way to find these slabs in less wind-affected areas. Shooting cracks and “whumpfs” (collapsing) are bullseye data that you’ve found unstable snow.

    Avoiding steep, wind-loaded slopes will reduce your chances of triggering an avalanche. Persistent slabs can break wider than expected and be triggered remotely—from areas below, above, and to the sides of steep slopes. Be aware of the terrain you're in and what's above you. If you choose to enter avalanche terrain, you might consider avoiding slopes with terrain traps, rocks, cliffs, trees, and other obstacles that could increase the consequences of being caught in an avalanche.

    (12/21/2024) Skier-triggered avalanche near 9800' on a NE aspect in the northern Boulder Mtns.

Avalanche Discussion

Yesterday, the snowpack was not afraid to speak up. Observers reported a human-triggered avalanche near 9800 feet on a NE aspect in the northern Boulder Mtns and a booming snowpack collapse that sounded like a shotgun near Copper Mountain in the Banner Summit zone (NE aspect near 8800 feet).

The party involved in the avalanche reported "patchy" wind loading in the area and no obvious signs of instability before the slide. The avalanche released when the first skier was part-way down the slope, and they were able to ski out of it. We're happy to report everyone was okay. The trigger location of this avalanche - a few turns in rather than from the top - highlights the hard-to read character of persistent slabs. While the terrain was wind-affected, the lack of obvious wind-loading and no signs of instability demonstrate the tricky nature of persistent slabs.

The overnight snowfall hasn’t really changed the big picture of our persistent slab problem. Conveniently, the way in which we navigate the persistent slab problem also hasn’t changed:

  1. Avoid steep, wind-loaded slopes.
  2. Keep a close eye on your slope angles; if you're trying to avoid avalanche terrain, make sure you're doing so.
  3. Be aware of the terrain you’re in and connected to - especially what's above you.

The new snow has, unfortunately, made identifying wind-loaded slopes more challenging by covering up the old snow surfaces and obvious textures. All recent avalanches have failed in windy areas, which is why you’ve continued to hear us discussing it.

So how do you find the wind slab-weak layer combo now that you can’t easily see it? Quick hand-pits, probing, digging or simply jumping off your sled into undisturbed snow are easy ways to leverage your curiosity and feel for slabs of firmer snow over weaker layers. Tracking the locations of these slabs is a solid move for you and your backcountry partners looking to the future with a stormy week ahead.

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