Avalanche Forecast
Issued: Feb 19th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
MBender,
Avalanche Canada
Snow will continue to accumulate Friday night and through the day Saturday. The load on a buried persistent weak layer is gradually increasing and may well reach a tipping point. Check out our Forecaster Blog for a more detailed explanation of the brewing situation.
Summary
Confidence
Low - Forecast snowfall amounts are uncertain. Uncertainty is due to whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather.
Weather Forecast
FRIDAY Night: Cloudy with flurries, accumulation 3 to 8 cm, 60 km/h southwest wind, alpine temperature -8 C.
SATURDAY: Cloudy with snowfall, accumulation 5 to 10 cm, 40-60 km/h southwest wind, alpine temperature -7 C.
SUNDAY: Snow, accumulation 15-25 cm, 50-90 km/h west and southwest wind, alpine temperature -2, freezing level 1700 m.
MONDAY: Cloudy with flurries, accumulation 5 cm, 40 to 60 km/h southwest wind, alpine temperature -4 C.
Avalanche Summary
A few wind slab avalanches were triggered by riders in the north of the region earlier in the week.
The likelihood of triggering new wind and storm slab avalanches will increase quickly as the snow falls and the wind blows into the weekend. This is a good time to dial back your terrain choices, with some uncertainty on if/when the buried weak layer will become reactive.
Snowpack Summary
New snow and strong wind will form both wind and storm slabs on Friday night and Saturday. The wind is forecast to blow from the southwest, so watch for the deepest and touchiest deposits in lee slopes near ridges at treeline and alpine elevations. The air temperature is forecast to be quite a bit warmer than the past week, so slabs are anticipated to develop quickly.
The snow will load a widespread persistent surface hoar layer. Prior to the storm, the layer was 60 cm deep near Renshaw, 40 cm deep around Torpy and McBride, and 15 to 25 cm deep further north. Reports suggest this layer is most prevalent around treeline elevations, but likely reaches into the alpine and down into the trees too. It may sit above a crust below 1600 m. The likelihood of triggering this layer will increase as the snow turns into a cohesive slab.
There are presently no deeper concerns in the snowpack.
Terrain and Travel
- Watch for avalanche hazard to increase throughout the day.
- Wind slabs are most reactive during their formation.
- Dial back your terrain choices if you are seeing more than 20 cm of new snow.
- Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
- Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
Problems
Storm Slabs
New wind and storm slabs will form as the snow falls and the wind blows on Friday night and Saturday. The wind is forecast to be strong and from the southwest, so use particular caution near ridges in lee terrain features. As the snow accumulates in sheltered areas, new storm slabs may develop on all aspects and at all elevations.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
Snow and an overall warming trend may make a weak layer of surface hoar that developed late-January reactive to riders. Prior to this storm, the layer was found 15 to 60 cm deep across the region, being deepest in the south and shallowest in the north. This layer has been the most sensitive right at treeline, but it may extend up into the alpine, and be found in openings in the trees below treeline. The likelihood of triggering this layer is expected to increase once a cohesive slab develops above it.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Feb 20th, 2021 4:00PM
