Avalanche Forecast

Issued: Jan 2nd, 2017 4:09PM

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

triley, Avalanche Canada

Northwest Inland.

Expect change to be slow. Wind slabs will be slow to bond, and deep persistent weak layers will continue to be a concern for large avalanches.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Some thin high cloud overnight with strong northeast winds. Cold and clear on Tuesday with temperatures 5-10 degrees warmer in the alpine than in the valleys. Cold and clear on Wednesday with light-moderate northerly winds, some chance of a weak above freezing layer in the alpine. Cloud developing on Thursday with moderate westerly winds and no new precipitation.

Avalanche Summary

In the north of the region near Ningunsaw there was a natural avalanche size 3.5 that released in the basal facets on Monday. This is a good reminder that large full depth avalanches are possible in shallow snowpack areas. A natural avalanche cycle with slides up to size 2 occurred Friday in the mountains near Smithers. This was in response to the strong northerly winds. Wind slabs will likely remain touchy throughout the forecast period, as sustained winds redistribute any loose surface snow. Deeper persistent weak layers will also remain a concern, it is possible to trigger large avalanches.

Snowpack Summary

Snowpack depths in this region are still shallow - around 1 m or so, meaning there are a lot of weak sugary facets in the snowpack. Recent storm snow is being redistributed by strong to extreme winds, and wind slabs are widespread behind exposed features. Where hard wind slabs overlie weak facets, the structure is ripe for human-triggered avalanches.In addition to the sugary facets, you may find a layer of feathery surface hoar (up to 15 mm in sheltered areas), buried around 20 - 30 cm below the surface. There is another weak layer that formed during the early December cold snap which is now about 40-60 cm deep. A crust from mid-November may be found close to the bottom of the snowpack nestled in amongst the facets. We don't have a lot of information about these layers, but it's worth noting the layer responsible for most of the large avalanches during the big storm just before Christmas was the mid-November rain crust.

Problems

Wind Slabs

Extreme winds will continue to redistribute loose surface snow into reactive wind slabs. Watch for areas that were previously scoured and may become reverse-loaded by northerly winds.

Be cautious as you transition into wind affected terrain.Avoid travelling in areas that have been reverse loaded by winds.Use ridges or ribs to avoid pockets of wind loaded snow.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Deep Persistent Slabs

40-60 cm of recent snow sits above a weak, faceted lower snowpack. This fundamentally weak snowpack structure supports human-triggered avalanches from places like convex slopes in shallow areas, and is likely to persist for some time.

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 - Likely

Expected Size

2 - 3

Valid until: Jan 3rd, 2017 2:00PM