Avalanche Forecast

Issued: Dec 11th, 2015 10:16AM

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

ghelgeson, Avalanche Canada

Purcells.

The trees are NOT a safe haven right now as a persistent weak layer at lower elevations is sensitive to human triggers. Increasing winds Saturday may form touchy wind slabs in the alpine too.

Summary

Confidence

Low - Timing, track, or intensity of incoming weather system is uncertain on Sunday

Weather Forecast

We've reached the end of the high impact storm train. A rather mundane system drifts into the region Saturday night and then we're looking at high pressure for at least a few days. SATURDAY: Trace of snow during the day. Freezing level holding around 800m. Winds expected to be light SW for most of the day, increasing to Moderate SW in the afternoon. SATURDAY NIGHT: Freezing level 600m, moderate to strong SW winds, 2 to10cm of snow. SUNDAY: Freezing level rising to 1200m. Moderate SW winds. 1 to 5cm of snow expected. MONDAY: No snow expected. Freezing level at valley bottom. Light NW winds.

Avalanche Summary

Control work in the central and southern Purcells Thursday produced avalanches to size 3.5 on a variety of aspects, some of which ran full path. On Friday a skier accidently triggered a size 2.5 avalanche on an east facing feature at 1500m in the northern Purcells. This avalanche failed on the early December Persistent Weak Layer.

Snowpack Summary

A string of storms that began on December 2nd has produced 35 to 80cm of storm snow in the Purcells. You may find a brittle crust about 20 cm below the snow surface as high as 2000m that was formed by rain and warm temperatures last Tuesday. Below all the new snow lies the early December persistent weak layer. This weak layer manifests as an old sun crust on due south facing features in the alpine, and large grained surface hoar below 1800m and small facets in isolated pockets. The surface hoar is the major player and it's been most reactive below treeline between 1400 and 1800m. Recent winds out of the southwest have formed wind slabs on lee features that are mainly confined to the alpine, but you may find the odd fresh wind slab at treeline too. The mid and lower portions of the snowpack are thought to be well settled.

Problems

Persistent Slabs

A layer of buried surface hoar can be found 35 to 80cm below the snow surface and is expected to be most sensitive to human triggering below treeline between 1400 and 1800m. Plan to travel below treeline as conservatively as possible.

Avoid open slopes, convex rolls, burns and cutblocks below treeline where buried surface hoar is best preserved and most volatile.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 5

Storm Slabs

New snow is expected to remain sensitive to human triggers. Storm slabs are thought to be especially deep and weak around alpine terrain features like the leeward side of ridge crests, terrain breaks, and wind-loaded chutes.

Avoid freshly wind loaded features and use ridges or ribs to travel around these problem areas.>Start with simple terrain options and take a curious approach to the snowpack. You may be able to step out into some challenging terrain at and above treeline after learning more about the snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Valid until: Dec 12th, 2015 2:00PM