Avalanche Forecast
Issued: Dec 18th, 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.
zryan,
Avalanche Canada
Saturday's storm created storm slabs in the alpine and treeline that will likely still be reactive to human triggering. Anticipate larger, more reactive slabs in wind loaded areas. Uncertainty exists around a buried persistent weak layer. Learn more about how to manage it here.
Summary
Confidence
Moderate - Forecast precipitation (either snow or rain) amounts are uncertain. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Saturday Overnight: 5-25 cm of new snow, tapering into the morning. Strong southwest winds easing to moderate and shifting west. Alpine temperatures dropping to around -13 C.
Sunday: Partially cloudy with light flurries, trace to 5 cm of accumulation. Light northwesterly winds and alpine temperatures around -16 C.
Monday: Partially cloudy with a chance of light flurries. Winds increasing throughout the day, moderate from the west. Alpine temperatures around -16 C.
Tuesday: Mainly clear, moderate west winds at ridgetop. Alpine temperatures rising to around -13 C.
Avalanche Summary
On Saturday, operators reported reactive wind slabs developing throughout the day.
On Friday, operators in the eastern Purcells triggered several size 2-2.5 deep persistent avalanche with explosives on N and NW aspects in the alpine.
Snowpack Summary
Yesterday, we received 20-40cm of new snow accompanied by strong to extreme southwest winds. Storm slabs are expected to have formed in the alpine and treeline. In wind exposed areas strong southwest wind will have been the dominant feature, transported the new snow into deeper deposits in lee features.Â
Below this new snow, consolidated snow from the previous week's storm sits over a substantial crust that formed in early December. This crust is 10-30 cm thick and can be found down 60-120 cm. It is present across aspects below 2300m. A thin layer of weak facets (sugary snow) can found above this crust that has demonstrated reactivity in snowpack tests and recent avalanche activity.Â
A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. Although this layer has been trending less reactive, it remains on our radar.
The snowpack depth at treeline is around 115-200 cm. The deepest snowpack can be found near the Bugaboos.Â
Terrain and Travel
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
Problems
Storm Slabs
In the past 24 hours we have received 20-50cm of new snow. This will have created reactive storm slabs in the alpine and treeline. Anticipate larger, more reactive slabs in wind-drifted areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A layer of weak facets (sugary snow) can be found down 50-100 cm over a crust that formed in early December. This layer is starting to produce avalanches across the province and this storm may be the tipping point to start seeing both natural and human triggered large destructive avalanches.
At the base of the snowpack above 2200 m, a layer of depth hoar lingers. Avalanches-in-motion have the potential to step down to this layer.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 19th, 2021 4:00PM
