Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

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2 · Moderato
Limite del bosco
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

You could trigger an avalanche in areas of recently wind-drifted or pillowed snow. It'd be a stroke of bad luck but triggering an avalanche on weak layers buried 4-6 feet deep remains a possibility 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

    A stiff west wind and light snowfall this morning may combine to form fresh, sensitive wind slabs. These thin slabs will build upon older, stiffer slabs that formed during Tuesday afternoon's gusty NW-NE wind.

    You're most likely to encounter this problem at upper elevations. Wind slabs commonly form downwind of prominent terrain features like ridgelines or mid-slope gullies. Watch for smooth pillows of stiff or hard snow, dunes, or wave-like patterns on the surface. These slabs may be sensitive where they overlie hard, wind-polished surfaces or crusts. Cracks shooting out from your skis or sled are a sure sign that you've found a sensitive slab. 

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    The weak layers we've struggled with all winter have not gone away but they've become less reactive to the weight of a skier or rider. Triggering a 4-6 foot thick persistent slab avalanche is becoming increasingly unlikely. Unlikely, however, is not the same as impossible. It would take a dose of very bad luck, but it may be possible to trigger one of these monsters in very steep (over 35 degrees), wind-swept, alpine terrain.  

    On Tuesday, I checked out an avalanche that failed on an east-facing slope near 8800' on Copper Mountain in the Banner Summit Zone. This slide (photo, observation) likely failed over the weekend and released on a subtle weak layer beneath our last storm snow.  Limited direct observations of this layer suggest that it's not likely an issue in the near term. That said, it's worth taking the time to dig a quick pit to see how recent snow is bonding to the older snow below.

Avalanche Discussion

LOW Danger: The Banner Summit and Wood River Valley & Soldier Zones are at LOW danger. When the danger is LOW triggering an avalanche is unlikely and most slopes are safe. Could you trigger an avalanche at LOW danger? Certainly, but you'd have to find one of the very few spots in the range with unstable snow. If you dropped 50 people off and told them to ski or ride the steepest, wind-loaded slopes they could find, 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 altogether.

Looking Ahead: A passing cold front this morning will kick off a blustery, cold, and snowy weekend. Snowfall amounts in the next couple of days will be light, but it can be surprising how quickly fresh slabs can form with a persistent wind. Snowfall will increase Saturday night and weather models predict around a foot of new snow in some portions of the Banner Summit and Sawtooth & Western Smoky Zones by Sunday afternoon.

Our field objectives over the last couple of days included checking in on the snow surface to get a better sense of what this snow will rest on. You can read Chris and Martins' thoughts from yesterday near Williams Peak in the Sawtooth Mountains here. They concluded, "I could see some potential instability with the weekend storm but it doesn't seem likely that it will be extensive or long-lived in this area. "

Wednesday, in the Soldier Mountains, the conditions were very different. I found an ugly and relatively widespread crust and facet combination at middle elevations (video). Warm temperatures at the end of January and early February built a stout crust. Since then–unlike the snowier regions to the north–the Soldiers received very little snow. In sheltered areas, this tiny amount of snow was allowed to facet and surface hoar sprang up on shaded slopes. 

I highlighted these two examples to help point out the spatial variability we might expect with this weekend's storm. By late winter and spring, temperatures near or above freezing, heavier and more localized precipitation events, and strong solar radiation can produce a wide range of conditions over a short distance, not to mention zone-to-zone. As you head out to enjoy the snow, keep this variability in mind and frequently check-in to see how the new snow is bonding with the old snow surface. 

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