Daytime warming persists. Windslabs sit on a variety of storm interfaces, solar and melt- freeze crusts. Be very cautious in terrain where these slabs are sitting on crusts as these windslabs will be quite touchy until temperatures cool off.
Confidence
Moderate - Wind speed and direction is uncertain
Weather Forecast
Mainly cloudy with scattered flurries with a few centimetres of snowfall. Temperatures in the alpine will be -4.0 with freezing levels forecast for 1600 meters for Sunday. Winds will be out of the southwest light to moderate with some gusts to 60km/h.
Avalanche Summary
Observations were limited today but the high freezing levels will have caused some pin wheeling and likely some loose wet avalanches from lower treeline and below treeline on steeper slopes. Forecasters were called out to a rescue today which terminated our trip to the Commonwealth area prematurely. There were some windslabs up to size 2.0 on the recently buried crusts and isolated natural or cornice triggered deep persistent slabs up to size 3.0 in Banff National Park.
Snowpack Summary
Moist snow exists today up to 2300 meters on all aspects and elevations. There is 15-25cm overlying the March 8th interfaces (melt-freeze crusts and sun crusts). The upper snowpack is settling rapidly with the mild temperatures. In the alpine and upper treeline, wind slabs have been developing over the past few days and extra caution will be required where the wind slabs overlie the March 8th crust interface. The January 6th facets interface is showing improvement but large avalanches up to size 2.5-3.0 are still occurring on the interface so it persists as a layer that is low probability/high consequence avalanche problem.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.