Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Dangerous avalanche conditions exist. Triggering 1-3 foot thick avalanches is likely today.  Avalanches will be easier to trigger in terrain affected by the wind, but are possible in sheltered terrain as well. Avalanches can be triggered from long distances above, below, and to the sides of steeper slopes. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1.5–2.5

    What is it? Layers of weak snow in the upper snowpack can produce large, wide, 2-3' thick slab avalanches. Last week Ben spotted a large avalanche on Copper Mountain. It broke about 2 feet deep on a layer of weak facets. The slide appeared to have been remotely triggered by a skier on a low-angle ridge above a steeper slope (photo of the triggering track and crown). While the avalanche was initiated in wind-loaded terrain, crowns opened up in apparently sheltered terrain as well (photo at right/above).

    Where is it? The depth of these weak layers varies from slope to slope, but it's safe to assume that they exist on most slopes. The sensitivity will be amplified in wind-affected terrain (picture to right/above) in more exposed terrain. It is also possible to trigger slides in more sheltered locations as well.

    How can you recognize it? Shooting cracks and collapsing are clear signs of an unstable snowpack.Natural and human-triggered avalanches will offer guidance on what type of terrain and slopes these avalanches are likely to be triggered on, but it's safe to assume that they exist on many slopes.  It might take some digging into the snow to reveal previous wind-affected layers that the new snow has masked in more sheltered locations. 

    How can you manage it? Persistent weak layers can fail unpredictably and break significantly wider and deeper than you might expect, producing much larger avalanches. Today I recommend you choose simple, conservative terrain to play in. Pay close attention to the terrain around you and what you are connected to in slope steepness. The combination of a recent large natural avalanche, an ugly snowpack structure, and unstable snowpack test scores is plenty of evidence to keep me out of big, steep, complex avalanche terrain.

    (2/28/2023) NE face of Copper Mountain at 8,400'. This avalanche appeared to be remotely triggered by a skier from above. This crown in sheltered terrain points to the potential for encountering avalanche problems outside of areas that are obviously affected by the wind.

  • Wind Slabs

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

    What is it? Recent snow and winds have created sensitive 1-2 foot thick slabs in exposed, upper-elevation with wind-affected snow.

    Where is it? These slabs will be the largest and thickest at upper elevations. Be on the lookout for wind slabs near ridgelines and on the sides of mid-slope features like gullies and ribs.

    How can you recognize it? Cracks shooting out from your skis or sled and collapsing clearly indicate instability. Look for ripples in the snow, dunes capping ridgelines, and drifting along gulleys or chutes' sides. Wind-deposited snow will be stiffer and keep your skis or snowmobile on or closer to the surface. Some of these slabs might be masked by recent snow and be more hidden.     

    How can you manage it? Wind slabs that fail can effectively trigger deeper weak layers described above. Seek more sheltered locations and follow the terrain management listed in problem #1.

    (2/28/2023) This large avalanche was observed on a N aspect of Copper Mountain near Banner Summit. The crown extends into terrain that is mostly sheltered from the wind.

Avalanche Discussion

Now is the time to be conservative. Don't let the light, fluffy powder lure you into avalanche terrain. The steeper slopes you may have played on last week look much different now. The warning signs are showing themselves in various ways. Recent skier and rider-triggered avalanches should be the biggest red flag, but evidence of natural avalanche activity solidifies this point (see the Avalanche Database).

Pay close attention to the terrain around you and what you are connected to in slope steepness.  Slopes can release while approaching them from below on more mellow terrain. Pockets of slopes steep enough to slide have proven to be enough to cause avalanches, like the one on Baldy "out of bounds" (report), Olympia Gulch off Paterson Peak (report), Quigley Canyon (report), East Fork of Baker Creek (report) and Della Mtn. (report). Cliffs, trees, rivers, and other terrain traps magnify the consequence of even small slides.

Persistent slabs are notorious for not always failing while the first person plays on the slope. Sometimes it will take the next person or the last member of the group to find that "sweet spot" in the snowpack that causes the whole slope to become unglued. Luckily, the terrain in the surrounding mountains offers non-avalanche slopes to have loads of fun on right now. Double-check while measuring slope angles, and when in doubt, err to the side of caution by calling it steeper than you might think. Treat slopes with avalanche terrain with respect and give them a wide berth. 

Regioni coperte