Avalanche Forecast

Issued: Jan 12th, 2017 4:09PM

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

jfloyer, Avalanche Canada

Northwest Inland.

The storm this weekend is currently expected to only bring light amounts. Danger is still expected to rise on account of strong winds and rapidly rising temperatures.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Saturday

Weather Forecast

Friday: Flurries. Ridgetop winds increasing to around 70 km/h from the southwest. Temperatures rising from around -20C in the morning to -10C in the afternoon. Friday night: Up to 5 cm new snow with continued strong winds and rising temperatures.Saturday: a further 5 cm new snow expected, ridgetop winds around 70 km/h from the southwest and treeline temperatures touching 0C. Freezing level expected to be around 1200 m.Sunday: A break in the storm with flurries, winds around 40 km/h from the southwest, freezing level around 1200 m.

Avalanche Summary

On Tuesday, a skier accidentally triggered a size 2 wind slab on a 34 degree southwest facing slope at treeline. This avalanche occurred a few kilometres east of the Kispiox river valley. A natural avalanche also ran about that time near Ningunsaw. It was reported as a size 2.5 running on basal facets on a southwest aspect at 1700 m.

Snowpack Summary

Recent wind transport has shifted low density snow into wind slabs at upper elevations. Recently temperatures have been warmer in the alpine than in the valley, which may have made the alpine snow slightly firmer (in sheltered locations - it's already firm where it's been drifted by wind). Snow depth at treeline varies from about 1 m in most areas to 2 m in deeper snowpack areas in the south and west of the region. The shallow snowpack areas mostly consist of weak facetted or sugary grains beneath hard slabs. These hard slabs may produce surprisingly long fractures resulting in large avalanches, and in some instances they may step down to weak faceted snow crystals near or at the ground. In addition to the facets, a thick layer of buried surface hoar may be found 30-40 cm below the surface. There is another persistent weakness that formed during the early December cold snap which is now about 50-70 cm deep.

Problems

Deep Persistent Slabs

In most areas this is a lower probability, high consequence scenario and requires a conservative approach to larger terrain features. Avoid likely trigger spots such as steep and rocky areas with a shallow snowpack.

Avoid steep convexities or areas with a thin or variable snowpack.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Wind Slabs

Strong to extreme winds may redistribute any remaining loose surface snow into fresh wind slabs, adding to an ongoing wind slab problem. Wind slabs may step down to deeper weak layers resulting in surprisingly large avalanches.

Avoid areas where the snow feels stiff or slabby.Be cautious as you transition into wind affected terrain.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Jan 13th, 2017 2:00PM