Archived

Avalanche Forecast

Dec 31st, 2016–Jan 1st, 2017

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Alpine

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Purcells.

Fresh wind slabs are forming at higher elevations, and have the potential to step down to a lingering persistent weak layer. Watch for signs of instability and choose conservative routes.

Confidence

Moderate - Wind speed and direction is uncertain

Weather Forecast

SUNDAY: Morning flurries easing off in the afternoon, moderate northeast winds, alpine temperatures around -18.MONDAY: Mix of sun and cloud, light east winds, alpine temperatures around -22.TUESDAY: Sunny with cloudy periods, light east winds, alpine temperatures around -18.

Avalanche Summary

On Friday, there were numerous reports of size 2 avalanches including natural and skier-triggered loose dry avalanches and explosive-triggered wind slabs. There were also isolated reports of size 2 storm slabs on Saturday, including one that stepped down to glacial ice on a steep south-facing slope. Expect touchy wind slabs to develop as moderate winds redistribute loose snow in exposed terrain.Also, a notable MIN report from Friday shows what seems to be a size 2 persistent slab that was triggered by a ski cut in a cutblock west of Kimberly (see MIN report from Mallandaine Pass). This is a reminder that although avalanche activity on persistent facet layers has been intermittent, the problem will likely linger for some time in shallow snowpack areas.

Snowpack Summary

The region received a total of 40-60 cm of low density snow over the past week. Recent winds have come from a variety of directions and have loaded leeward and cross loaded features in exposed terrain. An interface that formed during the early December cold snap can be found buried 40-80 cm deep. The interface may consist of stiff wind-affected snow, faceted (sugary) crystals, or surface hoar crystals. The overlying slab appears to have a poor bond to the interface in some areas, such as wind-affected terrain in the Dogtooth range and shallow snowpack areas like the southern Purcells. The thick mid-November crust and facet layer is now buried 70-150 cm deep and appears to be dormant.

Avalanche Problems

Wind Slabs

Wind slabs can be expected on all aspects as winds will shift from the southwest to the northeast.

Use ridges or ribs to avoid pockets of wind loaded snow.Be cautious as you transition into wind affected terrain.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 2

Persistent Slabs

40-80 cm of snow sits above a weak layer of facets from mid-December and continues to be reactive in parts of the region that have thinner snowpacks.

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.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 3