Bollettino valanghe

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
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

The chances of triggering an avalanche are great enough that skiing or riding steep slopes remains a risky proposition. Wind-affected terrain is the most dangerous, but avalanches could occur on sheltered slopes too. You could trigger avalanches remotely—from gentler terrain above, below, and to the sides of steep slopes. To reduce your risk, choose lower-angled terrain that is not directly below large avalanche paths. 

Problemi valanghivi

  • Persistent Slabs

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

    Despite being well into spring, we're still dealing with mid-winter-style Persistent Slab problems (watch this video). Multiple weak layers exist in the snowpack that can be lumped into two distinct problems:

    1. "Fresh" Slabs: The April Fools storm produced numerous avalanches. Sunday, SAC forecasters remotely triggered multiple avalanches in neighboring zones (Banner Summit video), and an observer heard two natural avalanches release near Copper Mtn. These avalanches failed on crust + facet combinations or thin layers of small facets in the upper 2 feet of the snowpack. Due to the variable weather in March, the distribution of these weak layers varies greatly from slope to slope and across the zone.
    2. Older, Deep Slabs: While it would take a dose of bad luck, triggering a massive 3-5 foot thick avalanche on older, deeply buried weak layers can't be ruled out. The most recent deep slab avalanche occurred last Friday in the Frenchman Ck drainage near Smiley Ck when riders remotely triggered a slide that broke 4-5 feet deep and 800+ feet wide (photo at right/above). While triggering one of these beasts is far less likely than the "fresh" slabs above, the consequences would be devastating.

    Not one but two persistent slab problems? No thank you! This is a tough situation to manage. You may or may not see obvious signs of instability on unstable slopes, depending on the depth of the weak layer. Multiple skiers or riders might play on a slope before it avalanches. Reduce your risk by staying off of (and out from beneath) slopes steeper than about 35 degrees, especially those with evidence of wind loading.

    ADDITIONAL DISCUSSION: You may encounter wind slabs in exposed middle and upper elevation terrain. Slabs will be thicker and more widespread in alpine terrain. Any wind slabs that you encounter may be perched above weak facets and/or crusts, making avalanches easier to trigger and wider than you'd expect. Look for wind slabs near ridgelines, on the sides of gullies, and lower in cirques beneath large cliff bands and on the aprons of chutes and couloirs. Surface textures like dunes, ripples, or pillows are clues that the wind has been at work. 

    Cornices are unusually large this year. Give these unpredictable beasts plenty of space by traveling far from the edge, staying where you can easily feel dirt or rocks below your skis or sled. Large, falling cornice chunks and/or relatively small wind slabs moving downhill could trigger the larger, more dangerous Persistent Slab avalanches discussed above.

    (3/31/2023) Crown of a very large avalanche that was remotely triggered by riders from at least 500 feet away on the ridgeline above. It broke 4-5 feet deep and 800+ feet wide. This slope faces W at 9,300' in the Frencman's drainage near Smiley Creek. You can clearly see the two sets of persistent weak layers in our snowpack in this photo. 

Avalanche Discussion

This has been an abnormal winter. The unusualness is reflected in our well-above-average snowfall (currently around 150% of normal) as well as prolonged periods of unstable conditions. What Ben said earlier in the season still holds true now: this winter, we're either forming weak layers or burying them. We've had very few LOW danger days this season—ranging from a big fat zero in the Galena Summit & E Mtns zone to 10 in Banner Summit. On average, we tend to have 20-40 LOW danger days.

Almost all of our elevated danger has been the result of persistent slab problems. You're probably tired of seeing these in the forecast and dealing with the uncertainty they present when choosing terrain. I get it—and I am too! By spring, we usually get a respite from the mid-winter persistent weak layers, and our patience pays off when we're able to ski or ride the steep terrain we've been eyeing all winter. I hate to be the negative Nancy—but that is not how this spring is shaping up. 

Variable weather in March produced weak layers that are equally variable. How long the sun hit certain slopes, and where the skiffs of snow fell, have significant effects on the distribution and nature of our "newer" buried weak layers—especially the crust + facet combinations. Trying to tease out patterns of which slopes remain unstable is tricky at best and dangerous at worst. And then last Friday's very large, remotely-triggered avalanche in the Frenchman Ck drainage near Smiley Ck was a sobering reminder that our older, deeply buried weak layers haven't given up the ghost.

The good news is there is some incredible powder riding right now—rivaling even mid-winter conditions. By sticking to lower slope angles (less than about 35 degrees), watching for wind-loaded slopes, and avoiding the runouts of large avalanche paths, you can enjoy some all-time, late-season snow conditions.

Regioni coperte