Avalanche Forecast
Issued: Dec 8th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Deep Persistent Slabs.
shorton,
Avalanche Canada
Don't let the improving weather lure you into dangerous terrain. The new snow will likely need significant time to strengthen.
Summary
Confidence
Weather Forecast
We are entering a period of clear and cool weather.
TUESDAY NIGHT: Partly cloudy, light northwest wind, freezing level dropping to valley bottom and alpine temperatures drop to -10 C.
WEDNESDAY: Mostly cloudy, light west wind, alpine high temperatures around -5 C.
THURSDAY: Mix of sun and cloud, light wind, alpine high temperatures around -8 C.
FRIDAY: Mostly cloudy, light wind, alpine high temperatures around -8 C.
Avalanche Summary
As the weather clears we are uncertain about how quickly the recent snow will gain strength and bond to old interfaces. It likely sits atop a weak layer of surface hoar in wind-sheltered areas at treeline and at upper below treeline elevations (above the extent of the rain crust). At higher wind-affected areas it has likely formed thicker wind slabs.
With little in terms of field observations, a cautious and conservative approach to terrain is needed. Be aware of these new avalanche problems by looking for signs of instability like shooting cracks and whumpfs. Furthermore, an avalanche triggered in the upper snowpack could cause a larger deep persistent slab avalanche.
Our eyes and ears in the mountains are limited this winter due to fewer professional observations. If you go out in the mountains, please share your observations on the Mountain Information Network (MIN).
Snowpack Summary
Monday's storm delivered variable amounts of snow to the Cariboos with roughly 30 cm around Blue River and Valemount, 10 cm in the Robson Valley, and 5 cm around Barkerville. This new snow sits on top of a melt-freeze crust on south aspects and widespread surface hoar at treeline and below. Generally speaking, new snow does not bond well to these types of surfaces and will create a problem moving forward. Freezing levels were around 1300 m during the storm, so lower elevations are rain soaked and will form a crust on the surface.
A recent MIN report from the Barkerville area found a weak layer 30 cm below the surface. The lower snowpack is characterized by a couple of crusts, the most notable of which is sitting near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers on south facing slopes and in shallow, rocky areas in the alpine.
Terrain and Travel
- Choose conservative terrain and watch for clues of instability.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
- Be aware of the potential for large avalanches due to the presence of a deep persistent slab.
Problems
Storm Slabs
New storm and wind slab problems exist after Monday night's storm. In the Blue River and Valemount areas 30+ cm of snow sits above crusts and a widespread layer of large surface hoar. This has likely formed very reactive storm slabs.
There was less snow in other areas, but strong wind would have left reactive slabs on wind-loaded slopes and on steep convexities. These slabs may also sit above reactive weak layers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
A facet/crust layer sits near the base of the snowpack. For weeks it has sat dormant, showing no avalanche activity but producing the occasional snowpack test result. We are curious to see whether the weight of the recent snow will awaken this problem. Keep in mind that if a storm slab avalanche triggers/steps down to this layer, the resulting avalanche would be large and destructive.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 9th, 2020 4:00PM
