Avalanche Forecast
Issued: Dec 25th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
cmortenson,
Avalanche Canada
Strorm slabs will remain touchy with recent winds, new snow & an unstable buried layers. Let the snow stabilize before exposing yourself to any steep avalanche terrain - a small slide could step down to deeper weak layers. Happy holidays and enjoy the snow safely!
Summary
Confidence
Weather Forecast
Stormy snowy conditions will ease bringing mainly cloudy conditions with light snowfall accumulations and cool temperatures for the forecast period.
Friday night: Mainly cloudy, alpine high temperatures near -2C and freezing levels 200 m. Ridgetop wind light with moderate gusts from the southeast.
Saturday: Mainly cloudy with isolated flurries, trace to 5cm new snow. Alpine high temperatures near -3C and freezing levels 300 m. Ridgetop wind moderate from the East.
Sunday: Mainly cloudy with isolated flurries, trace new snow. Alpine temperatures near -4 and freezing levels 200 m. Ridgetop wind light and variable.
Monday: A mix of sun and clouds. Alpine temperatures near -4 and freezing levels 100 m. Ridgetop light and variable.
Avalanche Summary
We suspect a widespread natural avalanche cycle with the recent Christmas Eve storm that delivered 30-50cm of new snow with moderate to strong southwest winds that shifted east as the storm left. Human triggered avalanches remain likely, especially where wind has stiffened recent snow into windslabs or where storm slab sits atop weak layers.
On Friday morning reports of natural and explosive triggered wind slab avalanches to size 2. In addition, a very large (size 3.5) natural avalanche was reported from reverse loading from east winds. This MIN from the Shames back-country reports a couple small (size 1) avalanches.
On Thursday, numerous explosive triggered size 2 storm slab avalanches were reported. 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
30-50 cm of new snow fell across the region by Christmas Eve (Thursday). This recent snow has been transported by moderate to strong south/southwesterly winds that then shifted to the east as the storm left the region. 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 area and more recently in Shames back-country.
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.
Terrain and Travel
- Be aware of highly variable recent wind loading patterns.
- Be especially cautious as you transition into wind affected terrain.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
- Don't let the desire for deep powder pull you into high consequence terrain.
Problems
Wind Slabs
Fresh wind slabs will likely remain reactive, especially where they have been stiffened by the wind or where they sit atop a surface hoar layer that was reported from just before the recent storm. Initially with the recent storm, winds were from the southwest but then shifted to the east as the storm left the region. Thus all aspects near ridgecrest or wind affected terrain should be assessed for potential windslabs or buried windslabs.
Natural avalanche activity may begin to taper but human triggering remains likely. A 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 buried 30-60cm below recent storm snow. It seems to be very reactive in the Nass Valley, but also reported at ridgecrests and below in the Shames area. At the moment the reports are localized, likely includes two different layers & we are unclear where else it exists regionally. New snow is not expected to bond well to this surface hoar.
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 26th, 2020 4:00PM
