Avalanche Forecast

Issued: Dec 10th, 2016 3:47PM

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

rbuhler, Avalanche Canada

Sea To Sky.

Wind slabs should be expected in exposed terrain throughout the region on all aspects due to recently shifting winds. A weakness below the recent storm snow may increase the reactivity of these wind slabs.

Summary

Confidence

Moderate - Due to the number of field observations on Saturday

Weather Forecast

Light snowfall is expected to continue Saturday overnight and into Sunday. Weather models are currently showing another 5-15cm of snowfall by the end of the storm. On Sunday, freezing levels are expected to be at around 500m and alpine winds are forecast to be moderate from the southwest switching to northwest in the afternoon. On Monday, dry conditions are expected with a mix of sun and cloud. Treeline temperatures are expected to be below -10C and alpine winds should be light from the north. Sunny, dry, and cold conditions are currently expected for Tuesday.

Avalanche Summary

On Friday, one natural size 1 wind slab was reported. Ski cutting was also producing size 1 wind slabs in isolated terrain features that were loaded by recent strong northeast winds. A MIN post from Friday shows a 30cm thick wind slab which was triggered by a skier at treeline.Â On Thursday afternoon, strong winds resulted in a natural cycle of size 1-2 avalanches in steep wind-loaded alpine features.Â On Sunday, recently formed wind slabs are expected to be most reactive on north through east aspects from recent southwest winds. However, strong outflow winds on Thursday and Friday formed wind slabs on south and west aspects, and so wind slabs should be expected on all aspects in wind exposed terrain.

Snowpack Summary

High elevations were blasted with strong northeast outflow winds at the end of last week and are now experiencing moderate south winds and light snowfall. The result is extensive wind scouring and wind slab formation in exposed terrain. The new snowfall sits over a variable surface consisting of wind slabs, small isolated pockets of surface hoar, and surface facets. Expect the new snow to bond poorly with this interface. The mid-pack is generally strong, with a widespread mid-November crust buried 70-100 cm at treeline and anywhere from 30-200 cm in alpine terrain. Recent snowpack and explosive tests have shown the crust to be unreactive, but it could remain a problem in shallow alpine start zones.

Problems

Wind Slabs

Winds slabs may be lingering on all aspects due to recent winds from a variety of directions. These wind slabs may be sitting over a weak layer which is increasing the reactivity of these slabs.

Avoid freshly wind loaded features.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: Dec 11th, 2016 2:00PM