Avalanche Forecast

Issued: Dec 12th, 2015 8:03AM

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

rbuhler, Avalanche Canada

Kootenay Boundary.

Touchy fresh wind and storm slabs at higher elevations combined with lurking persistent weaknesses at lower elevations means you can't let your guard down this weekend.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

The last Pacific storm system is expected to hit the region Saturday overnight. 10-15cm of snowfall is expected with freezing levels around 1000m or so. Light scattered snowfall may continue through the day on Sunday. Alpine winds are expected be strong from the SW in the morning but will ease in the afternoon. Monday is expected to be dry with a mix of sun and cloud. Freezing levels are forecast to drop to near valley bottom and alpine winds should be light from the NW. Tuesday looks to be similar with mainly dry condition and a mix of sun and cloud.

Avalanche Summary

Reports from Thursday include an explosives-triggered 50cm thick persistent slab avalanche running on the early-December surface hoar on a convex roll below treeline in the Monashees.Â No new avalanches were reported on Friday.

Snowpack Summary

Recent heavy rain to treeline elevations and wet snow at higher elevations has saturated and loaded the upper snowpack, forming a thick crust which now has up to 20-25cm of fresh snow on top (with perhaps a thin crust within it). Weaknesses linger within the recent snow as well as at deeper old snow surface interfaces, which consists of facets, surface hoar, and/or a crust at upper elevations (especially on southerly aspects). The most critical of these weak layers is surface hoar buried early December (now down 70-100cm), which has the potential for remote triggering, extensive releases and prolonged sensitivity to triggers. It is likely lurking in most sheltered areas treeline and below. The thick mid-November crust is just under this weak surface hoar layer.

Problems

Storm Slabs

New snow will likely be sensitive to human triggers, and particularly deep and weak on the leeward side of ridge crests and terrain breaks, and in wind-loaded chutes.

On steep slopes, pull over periodically or cut into a new line to manage sluffing.>Be cautious as you transition into wind affected terrain.>The new snow will require several days to settle and stabilize.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

A layer of buried surface hoar can be found 70 to 110cm below the snow surface and has been most sensitive to human-triggering below treeline between 1400 and 1800m. Plan to travel below treeline as conservatively as possible.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Be alert to conditions that change with elevation.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Dec 13th, 2015 2:00PM