Avalanche Forecast
Issued: Jan 21st, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Deep Persistent Slabs.
ahanna,
Avalanche Canada
Southerly winds are forecast to build over the day Wednesday, forming touchy windslabs from recent storm snow.
Summary
Confidence
High - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.
Weather Forecast
Tuesday night: Overcast with isolated flurries bringing a trace of new snow. Light wind from the southwest. Alpine low -2 C. Freezing level around 800 m.
Wednesday: Overcast with isolated flurries bringing up to 5 cm of new snow. Winds building to strong south through the day. Alpine high -1 C. Freezing level around 1000 m.
Thursday: Heavy snowfall bringing 20-40 cm of snow with rain below 500 m, concentrated in the south of the region. Strong southwest winds, approaching extreme at ridgetop. Alpine high -3 C. Freezing level around 1000 m.
Friday: Heavy snowfall bringing 20-40 cm of new snow with rain below 500m, concentrated in the south of the region. Strong southwest winds. Alpine high -1 C. Freezing level around 1000 m.
Avalanche Summary
A widespread natural storm slab avalanche cycle up to size 3 was observed as the storm tapered off Monday. Reports of artificially triggered storm slab avalanches include remote size 1.5-2.5 near treeline. Explosive control work below treeline in the highway corridor produced results up to size 1.5.
Reports of deep persistent slab avalanches have been trickling in throughout the month. They are associated with a November crust layer near the base of the snowpack which has produced very large avalanches (size 3+) with crown depths of around 2 m. Observations are typically in alpine terrain, on lee or cross-loaded slopes.Â
Snowpack Summary
60-90 cm of recent snow is forming fresh windslabs as southerly winds build through the day Wednesday.
The new snow rests on extensively wind affected surfaces at upper elevations, and a thick layer of weak facets in sheltered areas treeline and below.
A deep crust from mid November lurks at the base of the snowpack. A few recent large avalanches have run on this layer on lee and cross-loaded features high in the alpine. This week's succession of storms adding significant new load to the snowpack will be a good test of this layer.
Terrain and Travel
- Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
- Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
- Wind slabs are most reactive during their formation.
- Be aware of the potential for large avalanches due to the presence of a deep persistent slab.
Problems
Wind Slabs
60-90 cm of recent snow is forming fresh windslabs as southerly winds build through the day Wednesday.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
Reports of avalanches on this layer have been sparse but it has produced some very large natural avalanches that seem to be most prevalent on alpine lee and cross loaded slopes. The previous storm followed by a wind event forecast for Wednesday will be a good test for the mid November crust that lurks at the base of the snowpack.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 22nd, 2020 5:00PM
