Avalanche Forecast

Issued: Dec 3rd, 2018 4:19PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Persistent Slabs.

cgarritty, Avalanche Canada

Kootenay Boundary.

Our persistent slab problem hasn't yet fully healed. Treat steeper slopes in sheltered areas with a healthy dose of skepticism - especially if they're sun-exposed. See our Forecasters' Blog for more help on managing the problem.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Monday night: Increasingly clear with lingering low level cloud. Light northwest winds, increasing to moderate in the alpine.Tuesday: A mix of sun and low level cloud. Mainly light northwest winds, increasing with elevation to moderate or even strong in the alpine and remaining elevated overnight. Alpine high temperatures to about -8 with a mild temperature inversion and slightly cooler temperatures at lower elevations.Wednesday: A mix of sun and low level cloud. Light north winds. Alpine high temperatures around -8.Thursday: A mix of sun and low level cloud. Light variable winds. Alpine high temperatures around -6.

Avalanche Summary

No new avalanches were reported in the last week. Two MIN reports from November 24th are worth your consideration though:This one describes a rider getting caught and carried in a small storm slab in the Ymir bowl area. This one details a group of riders triggering a large deep persistent slab avalanche in Meadow Creek which is in the neighboring South Columbia region. Multiple folks were involved, but thankfully everyone survived.Huge thanks to everyone posting to the MIN, please continue to do so here.

Snowpack Summary

The storm last weekend delivered 20 to 40 cm of snow that has settled out to about 30 cm of soft snow on the surface. At treeline, the total height of snow is now between 100 and 140 cm. At 40 to 80 cm below the surface there is a persistent weak layer that was buried on November 21st. This weak layer consists of surface hoar (feathery crystals) in most places, but may present as a sun crust on steep south facing slopes. This layer has shown ongoing but variable reactivity in snowpack tests in the past week. A MIN report from the Kootenay Pass area (link here) and a social media post (link here) from the Whitewater area on Thursday highlight some of the more concerning recent results. This surface hoar is thought to be widespread at treeline and it may be found in sheltered alpine features too.At the base of the snowpack is a thick melt-freeze crust that formed near the end of October. This crust has shown limited reactivity thus far, but observations are very limited.

Problems

Persistent Slabs

Storm snow from the past couple of weeks is consolidating into a slab that rests on a persistent weak layer 40 to 80 cm below the surface. This layer seems to be most prevalent at treeline, but likely extends into the alpine in sheltered terrain.

Back off if you encounter signs of instability such as whumpfing, cracking, or recent avalanches.Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 4th, 2018 2:00PM