Bollettino valanghe

Banner Summit

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
Alta quota
2 · Moderato
Limite del bosco
1 · Debole
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 7 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Recent winds continue to form and build slabs and drifts in upper elevation terrain. Be cautious on steep slopes where you find wind-drifted or pillowed snow. Slopes where you could trigger weak layers buried 2-6 feet deep are becoming few and far between, but it may remain possible on very steep, rocky, wind-affected slopes at upper elevations. 

Problemi valanghivi

  • Wind Slabs

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

    Erratic, gusty winds yesterday and last night transported snow in exposed terrain. On some slopes, the wind likley formed thin new slabs or built existing wind slabs. Yesterday, SAC staff observed some isolated cracking—but no avalanching—on steep middle and upper elevation slopes in the Banner Summit area. This problem will be most common in alpine terrain and at upper elevations where it remains possible to trigger slides on slopes over about 35 degrees in steepness. The slabs could be more sensitive to triggering where they overlie hard, wind-polished surfaces or crusts.

    Watch for smooth pillows of stiff or hard snow, dunes, or wave-like patterns on the surface. If you see cracks shooting out from your skis or sled, consider where even a small avalanche could carry you before riding that really steep slope. 

    Additional Discussion: Yesterday, SAC staff checked out an avalanche that failed on an east-facing slope near 8800' on Copper Mountain. This slide (photo below, Observation) appeared to release a few days ago on a subtle weak layer that may have involved some faceting. 

    The sleeping dragon in the basement: Triggering a 4-6 foot thick persistent slab avalanche has become very unlikely. The weak layers we've struggled with all winter have not gone away, but they're buried at a depth where they are very difficult to impact with the weight of a skier or rider. Hard to trigger is not the same as impossible—you'll do well to keep them in mind and continue to factor them into your decision-making, especially if you're playing in rocky terrain with thinner, variable snowpack depths.

     

Avalanche Discussion

LOW does not neccessarily mean NO: Today is the first day of the year with LOW danger at all elevations in any of our zones (Wood River Valley & Soldiers). What is LOW avalanche danger? Most slopes are safe, but not all slopes are safe. If you dropped 50 people off and told them to ski or ride the steepest, middle and lower elevation, wind-loaded slopes they could find in this zone, someone would probably trigger a slab avalanche. It's nearly impossible to definitively predict which slope(s) are "triggerable", but we can hedge our bets by thinking about the consequences of small avalanches where we're playing. If you don't like the looks of what's below you—trees, cliffs, roads or other terrain traps—then move to a different part of the slope or another area.

Today's canvas is tomorrow's problem: The recent spell of cool, sunny weather has created weak surface snow on some aspects and elevations. In mid-February in south central Idaho, the combination of the sun angle and cool, winter temperatures can produce excellent conditions for a process called near-surface faceting. At the snow surface, you'll notice a variety of crusts and "recycled powder" (facets) that sound and feel "hissy" when you're skiing or riding. If we get a decent shot of snow this weekend, we may see avalanche activity on relatively thin slices of the compass where the weak layer is "just right". Noting the variety of the snow surface today can help you wrap your head around how dramatically stability may change with minor changes in aspect or slope angle this weekend. 

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