Avalanche Forecast

Issued: Jan 3rd, 2017 4:06PM

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.

Watch for above freezing temperatures at higher elevations as a temperature inversion develops on Wednesday.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Mostly clear overnight with a chance of thin high cloud. A temperature inversion will result in alpine temperatures around -5, while valley temperatures will be closer to -15. Clear with moderate northeast winds on Wednesday and temperature inversion continuing. A narrow band at treeline may be above freezing during the warmest hours of the day. Cloud with southwest winds developing on Thursday. Strong southerly winds and a few cm of new snow on Friday.

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

Wind slabs continue to be a concern for human triggering. Recent extreme winds have stripped some exposed north and east aspects and created variable depth deposits on south and west aspects.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - 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.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Jan 4th, 2017 2:00PM