Strong winds on Saturday will continue to add new load to leeward features in exposed alpine terrain.Extra caution is required around and below large cornices during the heat of the day.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A weak storm pulse is expected to bring 2-4mm of precipitation on Saturday. Freezing levels are expected to be around 2000m or higher and alpine winds are forecast to be strong from the southwest. A bit of a break is expected Saturday afternoon or evening before a second storm system arrives Saturday overnight. 4-8mm of precipitation is expected by midday Sunday with freezing levels around 2300m and strong southerly winds in the alpine. Sunday afternoon and Monday are currently forecast to be dry and sunny.
Avalanche Summary
No new avalanches were observed on Thursday. On Wednesday, two natural size 1.5 storm slabs were reported from the north of the region. These were 30cm thick and released on an southeast-east aspect in the alpine. A natural size 1.5 loose dry avalanche was also reported in the north from an east aspect gully feature in the alpine. In the southeast of the region, several size 1 wind slabs were ski cut on north through east aspects at 1800-2100m elevation. These were 10-30cm thick on steep leeward features around ridge crests. Ongoing strong southwest winds are expected to continue to build wind slabs in leeward features in the alpine on Saturday. Cornices are expected to become weak with daytime warming and sun.
Snowpack Summary
15-25cm of recent storm snow with strong southwest winds have formed wind slabs in leeward features. The recent snowfall may overlie a sun crust on steep solar aspects or small surface hoar in isolated sheltered areas. The recent wind has also formed large cornices which are expected to become weak with the forecast warming and sun. Old weak layers can still be found in the snowpack but these layers are reported to be well bonded and triggering has become unlikely.
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.