Avalanche Forecast

Issued: Dec 29th, 2016 4:21PM

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

cgarritty, Avalanche Canada

Purcells.

A bit of new snow and sustained winds have kept our wind slab problem alive and well. In sheltered areas, new snow may be a thin mask over buried slabs.

Summary

Confidence

High -

Weather Forecast

Thursday night: 5-10cm of new snow with moderate to strong winds from the west.Friday: Mostly cloudy with isolated flurries and a trace of new snow. Winds light gusting to moderate from the west. Alpine temperatures ranging from -7 in the south to -14 further north.Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Winds light gusting to moderate from the west. Alpine temperatures around -12.Sunday: A mix of sun and cloud with no new snow. Winds light from the northeast. Alpine temperatures ranging from -12 in the south to -19 in the north.

Avalanche Summary

Limited avalanche control took place in the northern part of the region on Wednesday and produced several size 1.5-2.5 avalanches. Crown depths ranged from 20-40cm. These occurred at high elevations and are attributed to wind slabs that have grown with recent wind and snow loading. An ACMG Mountain Conditions Report from Christmas day describes a slab avalanche failing on a steep, north facing slope at 2100m. This avalanche remains relevant for having stepped down 110cm to the November crust. The size of the avalanche is unknown, but this speaks to the touchy nature of persistent slabs in the area. On Christmas eve, a skier was partially buried in a size 2 slab avalanche while skinning up a northeast facing slope at about 2000m. The failure plane of this avalanche is unknown although the depth (40cm) suggests the mid-December weak layer may have been the culprit. Check out the Mountain Information Network post for more details.

Snowpack Summary

Between 15-20cm of new snow has fallen in the past few days. Moderate southwest winds have been redistributing the loose surface snow into new wind slabs in exposed higher elevation terrain. A highly variable 20-80 cm of snow overlies the mid-December interface which consists of stiff wind affected snow, faceted (sugary) crystals, and surface hoar that formed in sheltered areas. The overlying slab appears to have a poor bond to these surfaces in some areas, especially in wind-affected terrain in the Dogtooth range and possibly Quartz Creek. In sheltered terrain, the overlying slab has remained soft. As it continues to settle and gain cohesion, we may start to see a more widespread persistent slab problem develop. The thick mid-November crust/ facet layer typically sits 70-140 cm down in the snowpack. Recent avalanche activity in the Dogtooth Range suggests this layer has woken up and has the potential for large avalanches. Check out this ACMG Mountain Conditions Report for more info: https://mountainconditions.com/reports/december-25th-dogtooth-range-november-crust-awakening

Problems

Wind Slabs

New wind slabs have been building over the week. In areas where recent winds remained light, new snow will mask buried slabs. Look for patterns of wind redistribution and slab character in the snow as you navigate from one slope to another.

The recent snow may now be hiding old wind slabs that were easily visible before the snow fell.Use ridges or ribs to avoid pockets of wind loaded snow.Be cautious as you transition into wind affected terrain.

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

The potential for the mid-December layer to produce large avalanches has not yet been written off. Check for reactivity at this layer in areas that might harbour buried surface hoar or a thin snowpack.

Be aware of the potential for large avalanches due to the presence of buried weak layers.Dig down to find and test weak layers before committing to a line.Choose conservative lines and watch for clues of instability, especially in the north of the region.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Dec 30th, 2016 2:00PM