Lawinenlagebericht

Galena Summit & Eastern Mtns

Sawtooth Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Veraltet — dieser Lagebericht ist 6 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Recent snowfall and windblown snow have added weight to a very weak snowpack, and it's possible to trigger avalanches 6-12 inches thick. These will be more likely on wind-exposed, upper elevation slopes—especially those that are getting drifted by today's wind. Triggering a smaller avalanche is also possible on very steep slopes in sheltered terrain. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Snowfall over the past week has formed a soft, 6-8" thick slab atop extremely weak, faceted snow that formed during the 3+ week dry spell since mid-November. Even this small load produced a number of relatively small natural and human-triggered avalanches failing on the old faceted snow surface. While many of these were thin and "pockety" in nature, avalanches large enough to bury people occurred in the Western Smokys, Sawtooths, and Banner Summit area where more snow fell. 

    Slopes where you could trigger a slide aren't widespread, and if you did trigger an avalanche it would likely be on the smaller side—that's why the danger hasn't (yet) bumped past MODERATE. But triggering ANY size avalanche is potentially dangerous, and as we begin to load this nasty weak layer, now is the time to be more careful instead of less. You can decrease the chance of triggering a slide by using extra caution in these areas:

    • Upper elevation terrain where wind-drifted has created a thicker slab atop the weak layer.
    • Steep slopes and convexities approaching 40 degrees, even in wind-sheltered terrain.
    • The western side of this zone where more recent snow has fallen.

    (12/17/2020) This large natural avalanche was observed on the E-NE Face of Eureka Peak in the nearby Sawtooth & Western Smoky zone. Crowns range in elevation from 9,500-10,000'.

Avalanche Discussion

For snow and avalanche nerds out there, every weak layer that forms in the snowpack provides an opportunity to learn and add to your mental database. Most of this learning happens when we see how a weak layer responds during loading events. 

The nearly month-long dry spell that ended December 11-13 left us with a faceted snow surface that is about as weak as it can get. Folks that regularly read the avalanche forecast or monitor our social media channels have likely seen the videos illustrating just how loose and sugary the surface became. But where the rubber hits the road is watching how these layers respond to loading. If we'd received a couple feet of new snow, predicting this would have been child's play. Instead, over the past week, we've added a soft, 6-12 inch thick slab atop the facet layer—and we've received a free lesson in just how little load it would take to make the weak layer reactive.

Even in areas that only received 6-8 inches of powdery new snow, small avalanches occurred on steep road cuts, and observers reported collapsing of the snowpack. In our northern mountains where the slab is 8-12 inches thick, natural avalanches were even more common and a few were large enough to bury or injure a person. Yesterday in the Banner Summit zone, my Extended Column Test fractured across the column twice while I was cutting it out. 

The weather forecast is calling for continued slow loading of this weak layer over the next several days. If we've learned anything so far, it's that this layer will respond poorly to added weight. But I'm suspect this layer has more lessons to pass along. I always like to say that when it comes to facet layers, our area provides one of the best learning environments anywhere!

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