Weather Forecast
Saturday night: 4 - 10 cm Sunday: Moderate SW ridge top winds easing throughout the day. Isolated flurries. 1500m temp: -5 Freezing level: SurfaceMonday: Light S ridge top winds. 1500m temp -9. No snow. Freezing Level: SurfaceTuesday: Light S ridge top winds. Treeline temp -12. No snow. Freezing Level: Surface
Avalanche Summary
We're starting to see the effect of the big winds midweek. We're getting observations from across the region of a recent natural avalanche cycle to size 2. These avalanches are coming from Alpine terrain facing NW, N & NE.
Snowpack Summary
In the last 72 hours storm snow totals in the north are between 30 - 50 cm while the south of the region has seen closer to 80 cm near the Purcell Wilderness Conservancy. This adds to the abundance of storm snow that's fallen in the last 10 days. Strong winds on Wednesday/Thursday wreaked havoc in the alpine creating wind slabs capable of failing as large avalanches. Cornices are also a problem at the highest elevations. The mid-pack is reported to be settling well. I haven't heard of any test results on the late November surface hoar in the last few days. The early November crust, near the base of the snowpack has also been inactive as of late. It's important to note that professionals are still cautious about these lingering persistent slab problems, but the likelihood of triggering is low. Be wary of steep complex terrain with a shallow snowpack, where triggering a persistent weakness is more likely.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.