Confidence
Fair - Timing of incoming weather is uncertain on Thursday
Weather Forecast
Tuesday: Isolated flurries expected, winds light from the south and alpine temperatures near -12.Wednesday: Isolated flurries, generally overcast, winds light to moderate from the southwest and alpine temperatures near -11.Thursday: No precipitation is expected, winds light from the west and alpine temperatures near -12.
Avalanche Summary
Recent reports indicate both natural and skier triggered avalanches to size 1.5 in wind loaded features. Cornices have also been reported to be touchy in the north of the region.
Snowpack Summary
In the last four days the north of the region received 30 - 50 cm while the zone closer to the Purcell Wilderness Conservancy received closer to 80 cm. A wind event from last week formed relatively deep wind slabs in the alpine. New snow combined with wind has formed fresh windslabs on the surface. 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 involving the late November surface hoar in the last five 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.