Avalanche Forecast

Issued: Dec 4th, 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.

The strength of the snowpack is improving slowly. Keep your guard up around steeper, sheltered slopes and rolls at treeline and above.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Tuesday night: Cloudy with clear periods. Light northwest winds.Wednesday: Mainly sunny with cloud lingering at lower elevations. Light northeast winds. Alpine high temperatures around -11.Thursday: A mix of sun and low level cloud. Light variable winds. Alpine high temperatures around -7, cooler at lower elevations due to a mild temperature inversion.Friday: A mix of sun and low level cloud. Light southwest winds. Alpine high temperatures around -5, cooler at lower elevations due to a mild temperature inversion.

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

Days of cold temperatures have been gradually transforming about 30 cm of aging storm snow left on the surface from storms and flurries over the past couple of weeks into a layer of faceted (sugary, cohesionless) snow. At treeline, the total height of snow is between about 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 may also extend into sheltered alpine features.At the base of the snowpack is a thick melt-freeze crust that formed near the end of October. Observations of reactivity at this crust have been limited, but it has acted as the failure plane in several recent large avalanches in the neighbouring South Columbias.

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 steeper open slopes and convex rolls at treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2

Valid until: Dec 5th, 2018 2:00PM