Avalanche Forecast
Issued: Feb 27th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Persistent Slabs and Deep Persistent Slabs.
LP,
Avalanche Canada
The winds have decreased in most of the region, but the extent of the windslab development at upper elevations is widespread. Reports from today and over the weekend show this problem continues to be reactive to human triggering.
Summary
Confidence
Moderate
Avalanche Summary
With improved visibility today, ski hills reported evidence of a widespread windslab avalanche cycle to size 2 over last weekend. Today, skiers on Wawa near Sunshine triggered a size 1.5 avalanche near the slide triggered on Saturday. Lake Louise conducted some heli bombing in previously uncontrolled terrain in West Bowl and Maintenance cliffs. They got results to size 2 with crowns 50-60 cm deep failing on an old snow surface, possibly one of the January interfaces.
Snowpack Summary
15-20 cm of recent snow overlays a facet layer from last week's cold snap which capped the 30-60 cm of storm snow received early last week. Last weekend moderate to strong W winds formed widespread windslabs at alpine and treeline elevations. These windslabs overlie the various Jan PWL interfaces of sun crusts, facets and surface hoar down 80-120 cm. The weaker Nov 16 basal facet layer is down 100-200 cm and still produces mod-hard sudden collapse test results. Deeper snowpack areas west of the divide have a stronger and more supportive lower snowpack than areas to the east.
Weather Summary
Tuesday, expect light winds, very light morning flurries and alpine temperatures to rise to near -10C.
For Wednesday expect partly cloudy skies with isolated flurries in the afternoon. Winds will increase through the day with values reaching 50-70 km/hr by Thursday.
Terrain and Travel Advice
- Make conservative terrain choices and avoid overhead hazard.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Cornice failure may trigger large avalanches.
Problems
Wind Slabs
Areas that have received more snow over the weekend (Sunshine) are seeing slabs failing on the facet layer created by last week's cold snap. This surface snow overlies the 20 to 80 cm storm snow that fell early last week with strong winds from multiple directions. This created extensive wind effect, fresh cornice growth, and wind slabs at treeline and above. In general, wind slabs are becoming less sensitive to triggering, but if triggered they may step down to deeper layers.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Three persistent weak layers formed in January are down 70-100 cm. The biggest concern is triggering these buried suncrusts on steep solar slopes, but weaker facets and isolated surface hoar can be found on the same interface on shaded aspects. Key an eye out for these layers in steeper terrain.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
Weak facets and depth hoar are present at the bottom of the snowpack in most places. Last week's storm overloaded this interface resulting in numerous large avalanches running long distances. The snowpack is slowly adjusting to the new load, but natural triggering is still a concern with ongoing wind loading and cornice failures, and human triggering is still possible especially in shallower snowpack or rocky areas.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 28th, 2023 4:00PM
