Avalanche Forecast

Issued: Nov 29th, 2018 5:35PM

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

ghelgeson, Avalanche Canada

Kootenay Boundary.

There is a lot of uncertainty with the buried surface hoar layer down 40 to 80 cm. Human triggered avalanches are most likely at treeline and on sheltered alpine features. See our new Fx'rs Blog here for some insight into managing this problem.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

We are slowly transitioning towards a period of pronounced high pressure. The forecast period is marked by cooler temps, very little precipitation and the potential for less cloud cover by the weekend. THURSDAY NIGHT: Freezing level around 800 m, light south/southwest wind, no significant precipitation expected.FRIDAY: Overcast, freezing level around 1200 m, light south/southwest wind, a few centimeters of snow possible. SATURDAY: Broken cloud cover, freezing level around 800 m, light variable wind, no significant precipitation expected.SUNDAY: Scattered cloud cover, freezing level around 500 m, light northwest wind, no significant precipitation expected.

Avalanche Summary

No new avalanche observations from this week. A MIN report from last Saturday (Nov 24) describes a rider getting caught and carried in a small storm slab in the Ymir bowl area. On that same day a group of riders triggered a large deep persistent slab 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 that arrived Sunday night delivered 20 to 40 cm of snow that has settled out to about 30 cm of soft snow. At treeline the total height of snow is now between 100 and 140 cm. 40 to 80 cm below the surface lies 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 been reactive in snowpack tests this week. Check out this MIN from Thursday that talks about it. This surface hoar is thought to be widespread at treeline and it may be found in sheltered alpine features too. A recent MIN report suggests that this layer was producing obvious signs of weakness at Kootenay Pass on Tuesday.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

The recent storm snow 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 too.

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.Smaller avalanches in motion may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Nov 30th, 2018 2:00PM