Lawinenlagebericht

Banner Summit

Sawtooth Avalanche Center
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Lawinengefahr

Wed
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

While not likely, you could trigger a 2-4 foot thick avalanche on some slopes. Unfortunately, any slide triggered has the potential to be very large and unsurvivable. Reduce your risk by choosing lower-angled terrain and avoiding obvious avalanche start zones. Avalanches may be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    A dense, 2-4' thick slab overlies weak layers of sugary facets and facet+crust combinations. The weak layers are most common on middle and upper-elevation slopes facing SE-E-N-W. These weak layers are not as well-developed (i.e. "bad") as further south, and as a result, the avalanche cycle in this zone was not as extensive. Still, observers reported numerous large to very large avalanches in the aftermath of the storm.

    Where does that leave us now? There is uncertainty surrounding how well the weak layers are adjusting to this unique loading event. Further, our conditions are best described as low probability/high consequence with the following characteristics:

    • You aren't likely to experience signs of instability such as cracking and collapsing.
    • Snowpack tests don't work well with dense slabs approaching 3' in thickness.
    • Multiple people might ride on a slope before it avalanches.
    • Any slide triggered could be large enough to be unsurvivable.

    While conditions in this zone are (relatively) less dangerous than further south, the uncertainty of how our snowpack is stabilizing and the possibility of triggering a catastrophic avalanche do not inspire confidence. Despite the MODERATE danger rating, a conservative approach remains the best bet. Stick to moderate slope angles (less than about 35 degrees), avoid obvious starting zones, and pay attention to what would happen if you triggered an avalanche.

    ADDITIONAL DISCUSSION

    • While weather stations didn't record impressive winds with yesterday's storm, I observed moderate winds transporting snow near Copper yesterday. Watch for fresh drifts in upper elevation, wind-exposed terrain.
    • Despite the wintry weather, spring is officially here. As such, even brief periods of sunshine today could be intense enough to trigger loose snow avalanches on steep, sunny slopes.

    (3/12/2023) This avalanche failed on a SE slope at 9000' in Lola Creek. Based on the aspect and the appearance of the crown, this slide likely failed on a layer of facets below a melt freeze crust.

Avalanche Discussion

Our "March Madness" left us with two things I really don't like: a high degree of uncertainty and the possibility of triggering a catastrophic, unsurvivable avalanche. 

Uncertainty. After the dust settled from the major loading event that occurred between March 9th and 16th, we were left with a whole new world to figure out. The ensuing avalanche cycle was historic and frankly mind-blowing (especially from Galena Summit south to the Wood River Valley), and that served as a starting point for our assessing the snowpack stability.  So clearly things were very unstable during and immediately after the storm. Since then, the pressing question has been: how quickly is the snowpack healing? That's proved a tough one to answer. Given the "instant" 2-4' thick slab, many of our traditional approaches to assessing stability fail us. Signs of instability such as collapsing and cracking quickly diminish, and stability tests don't work well with dense slabs approaching 3' in thickness. 

Unsurvivable avalanches. In the aftermath of the storm cycle, we recorded nearly 50 very large (D3 in size) capable of destroying a stick frame house. If you trigger one of these beasts, the odds of surviving it are very low. If you don't get beat up by dense blocks of snow in the slide, the avalanche debris may be so hard and deep that your partners will struggle to extricate you. Given just how meaty the slab is, even a smaller avalanche would be more dangerous than you might expect.

These two characteristics have most savvy backcountry skiers and riders (myself included) making conservative choices—sticking to simple, low-angle terrain, avoiding large starting zones, and paying close attention to the consequences of triggering an avalanche.

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