Avalanche Forecast

Issued: Dec 27th, 2016 5:34PM

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

jlammers, Avalanche Canada

Purcells.

The local avalanche danger may be higher in the north of the region where buried weak layers have recently produced large, destructive avalanches.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Wednesday: Light flurries / Strong westerly winds / Alpine temperatures of about -13Thursday: 5-8cm of new snow / Moderate southerly winds / Alpine temperatures of about -10Friday: Overcast skies / Moderate westerly winds / Alpine temperatures of about -12

Avalanche Summary

There were no new reports of avalanche activity on Tuesday. An ACMG Mountain Conditions Report from Christmas day describes a slab avalanche failing on a steep, north facing slope at 2100m. The avalanche initially failed 40cm down from the surface, and then 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 8-15cm of new snow has fallen in the past few days. Limited observations suggest there was little in the way of wind on Tuesday. However, strong winds forecast for Wednesday may redistribute the loose surface snow into new wind slabs in exposed higher elevation terrain. 20-50 cm of snow typically 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

Persistent Slabs

Recent avalanches show that persistent slabs are a concern in the north of the region. The mid-December weak layer has recently been reactive to human triggering and may still be capable of producing large, destructive avalanches.

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 - Likely

Expected Size

2 - 3

Wind Slabs

Strong winds forecast for Wednesday may redistribute loose surface snow into fresh wind slabs. Watch for triggering in exposed higher elevation terrain.

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

Possible

Expected Size

1 - 2

Valid until: Dec 28th, 2016 2:00PM