Avalanche Forecast

Issued: Dec 30th, 2016 4:01PM

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.

jlammers, Avalanche Canada

Northwest Inland.

Cold, northwesterly winds mark a change in wind direction, which will set up fresh wind slabs in new locations in exposed terrain.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Friday evening: 3-12cm of new snow / Extreme westerly winds / Alpine temperatures of -3Saturday: Lingering flurries in the morning with clearing in the afternoon / Extreme northerly winds / Alpine temperatures of -10Sunday: Clear skies / Extreme northerly winds / Alpine temperatures of -10Monday: Clear skies / Moderate northerly winds / Alpine temperatures of -3

Avalanche Summary

No new avalanches have been reported. Wind slabs will likely remain touchy throughout the forecast period, as sustained winds will redistribute the new low density snow. The additional load of new snow will also keep deeper persistent weak layers reactive, making it possible to trigger larger 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 at this time. Recent storm snow has been redistributed by the wind, and wind slabs are widespread behind exposed ridges. 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 15-25 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

Variable winds will redistribute light amounts of new snow into fresh wind slabs. Watch for areas that were previously scoured and may become reverse-loaded as the winds switch direction.

Avoid travelling in areas that have been reverse loaded by winds.Avoid freshly wind loaded features.Be cautious as you transition into wind affected terrain.

Aspects: North, North East, East, South East, South, South West.

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 - Likely

Expected Size

2 - 3

Valid until: Dec 31st, 2016 2:00PM