Persistent Slabs
- Hochgebirge
- Waldgrenze
- Unterhalb der Waldgrenze
- Wahrscheinlichkeit
- Likely
- Größe
- 2–3
The slow loading of the December facet layer has produced a well-established persistent slab problem across the entire forecast area. Each storm has produced a new round of avalanche activity, but last week's storm produced some impressively large avalanches in this zone as the weak layer becomes more deeply buried.
We're now faced with a particularly dangerous and long-lasting instability. The weak layer is buried 2-3' deep on almost every slope. Often there is a high degree of uncertainty surrounding persistent slab problems. Now is not one of those times. Yesterday in the southern Sawtooths, my partner and I experienced a large collapse on a mid-elevation slope. A snowpit on this slope revealed a dense, 2' slab over very weak facets. As we moved into the upper elevations, we found the same weak layer beneath a very hard, 3+' thick slab of wind-affected snow. Snowpack tests in both locations confirm that conditions remain unstable (see video below/right).
Conditions remain dangerous, and it's likely you'd trigger a large to very large avalanche on most steep slopes. The best—and often only—way to manage the persistent slab problem is by sticking to lower-angled terrain. Given the possibility of remote-triggering, you'll also want to avoid being below steep slopes.
WIND SLABS: Strong winds last week ravaged the snowpack, and we've had several more rounds of wind since the storm ended. Although wind slabs are becoming less reactive to the weight of a skier or rider, wind-loaded slopes will have more stress on the buried weak layer making them especially dangerous. If you do trigger a lingering wind slab, it could "step down", failing on layers deeper in the snowpack and becoming much larger than the initial avalanche.