Avalanche Forecast
Issued: Dec 24th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
swerner,
Avalanche Canada
Storm slabs will likely be touchy on Friday and could step-down to deeper weak layers, initiating large avalanches. Give the snow plenty of time to settle and stabilize before heading out to avalanche terrain. Wishing you a safe and fun holiday season!
Summary
Confidence
Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Uncertainty is due to the extreme variability of wind effect on the snowpack.
Weather Forecast
A little more snow for Christmas as the storm moves off and the snow stops early Friday afternoon.
Thursday Night: Snow 10- 15 cm. Ridgetop wind strong from the southwest.
Friday: Isolated flurries 5-10 cm. Alpine temperatures near -2 and freezing levels 600 m. Ridgetop wind moderate with strong gusts as its switching from southwest to East.Â
Saturday/Sunday: Unsettled conditions and cloudy with some flurries. Alpine temperatures near -5 and freezing levels 500 m. Ridgetop wind strong from the East.Â
Avalanche Summary
On Thursday, at the time of publishing numerous explosive triggered size 2 storm slab avalanches were reported.Â
On Tuesday reports from the Beaupre sled area and the Nass Valley showed that storm slabs were easily triggered by humans up to size two. Check out the MIN posts here. Reports indicate that the storm slab may be sitting on a weak layer of surface hoar down 40-60 cm which is why the slab is so touchy.
Please consider sharing your observations with the Mountain Information Network; even just a photo of your day helps. Thank you to those that have already submitted this winter!
Snowpack Summary
Up to 50 cm of new snow hit the region by Thursday with more forecast by Friday. Touchy storm slabs exist, especially where the snow has been stiffened by the wind and/ or sits above a recent surface hoar layer down 40-60 cm. The buried surface hoar has been evident in the Nass Valley riding areas. Check out the MIN here. I’m uncertain if this layer exists elsewhere in the region or if it's isolated to that valley.
A crust that was buried in early December is now down 100 cm plus and counting in the alpine but is closer to the surface at and below treeline elevations. Around this crust are facets and potentially surface hoar in sheltered areas. Storm slabs may step-down to this layer.
The early-November crust is buried around 170-200 cm at treeline. This crust may have weak and sugary facets above it in parts of the region. This layer is currently dormant but remains on our radar.Â
Terrain and Travel
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Stick to simple terrain and be aware of what is above you at all times.
- Don't let the desire for deep powder pull you into high consequence terrain.
Problems
Storm Slabs
Fresh storm slabs on Friday will likely remain reactive, especially where they have been stiffened by the wind. Natural avalanche activity may begin to taper but human triggering is likely. A very conservative plan and terrain selection is key while avoiding overhead hazards like fresh cornices and large avalanche paths.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
A weak layer of surface hoar is down 60-100 cm and seems to be very reactive in the Nass Valley. At the moment the reports are localized. I'm uncertain where else it exists regionally.
A crust that was buried in early December is now down 90-200 cm and counting. Around this crust are facets and potentially surface hoar in sheltered areas. Human triggered avalanches and storm slabs may step down to this layer.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 25th, 2020 4:00PM
