Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2–3
Triggering a 2-4' thick persistent slab avalanche is possible on steep slopes. Persistent weak layers (sugary facets, surface hoar, or crusts) exist on most aspects and elevations. The widespread nature of this problem is unusual. You're most likely to trigger one of these slides in recently wind-affected terrain.
Reports of snowpack collapsing are on the decline, and instability tests point toward a slowly stabilizing snowpack. But the simple fact that we have a slab over a weak layer of snow (poor structure) means the possibility of triggering a large avalanche remains. We're generally headed in the right direction, but we're not out of the woods yet. Remember that you could trigger slides remotely—from gentler terrain above, below, and to the sides of steep slopes. These avalanches may break wider than expected or higher on the slope above you.
Unfortunately, avoiding slopes steep enough to slide is the only way to effectively manage this problem. While your odds of triggering a large avalanche are decreasing, the consequences of triggering one are not. Sticking to lower-angled, wind-sheltered slopes is a tactic to effectively reduce your risk.
ADDITIONAL DISCUSSION: Extreme wind over the Solstice built sensitive slabs on some slopes. You're most likely to find them at middle and upper elevations but they also exist on isolated slopes down to the valley bottom. Drifts may still be sensitive to your weight where they sit atop a weak surface of crusts, facets, and/or surface hoar.
Today's warm weather combined with afternoon sunshine may release loose snow avalanches on slopes that face the sun. These should be fairly small but will pile debris deep enough to be of concern below large slopes or channeled terrain. Valley locations may see some rain this afternoon, and certainly this evening which will spread loose snow avalanche activity to all aspects.
(12/13/2022) Numerous large avalanches were observed in the Lake Ck Drainage N of Ketchum. This large avalanche is on a NW-facing slope at 8,400' near Triple Pk.