Avalanche Forecast

Issued: Mar 9th, 2017 6:39PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Storm Slabs and Persistent Slabs.

cgarritty, Avalanche Canada

Sea To Sky.

Fresh storm slabs are only half of the picture on Friday. Recent wind slabs and persistent weaknesses deeper in the snowpack still can't be trusted - especially with increasing load stacking up above.

Summary

Confidence

Moderate -

Weather Forecast

Thursday night: Periods of snow bringing 15-20 cm of new snow. Moderate to strong south winds. Friday: Continuing flurries bringing another 5-10 cm of new snow. Moderate to strong southwest winds. Freezing level to 1300 metres with alpine temperatures of -3. Saturday: Periods of snow bringing 15-20 cm of new snow. Moderate to strong south winds. Freezing level to 1300 metres with alpine temperatures of -3. Sunday: Flurries bringing 10-15 cm of new snow. Moderate to strong southwest winds. Freezing level to 1500 metres with alpine temperatures of -1.

Avalanche Summary

Reports from Thursday included further observations of reactive wind slabs in immediate lee terrain occasionally releasing to Size 1 under skier traffic and with ski cutting.Reports from Wednesday revealed widespread natural avalanche activity, with Size 1-2.5 releases noted throughout the region. North aspects were most active. Ski cutting and explosives control in the Whistler area yielded numerous results with crown fractures ranging from 20-40 cm deep. Loose snow sluffing from steep terrain was noted on both days. Looking forward to Friday, expect a return to natural storm slab activity and increased human triggering potential. Also, while the bond at mid-February interface remains questionable, the likelihood of large persistent slab avalanches will also increase as forecast snowfall and wind add load to the snowpack.

Snowpack Summary

Moderate to strong southwest wind over Tuesday and Wednesday have redistributed the most recent storm snow and formed new wind slabs in leeward terrain at higher elevations. Another 10-15 cm on Tuesday brought the typical storm accumulation in the past week to 60-100 cm. This snow has settled into a slab that sits over the mid-February weak layer which consists of facets and/or surface hoar overlying a thick crust. In wind loaded terrain, this layer may be down 150 cm or more. Recent observations suggest this layer is still reactive and capable of producing wide propagations if triggered. We have been in an incremental loading scenario over the past week and this layer has not yet been fully tested. Expect it to wake up during the storm on Friday. Below the crust layer, the mid and lower snowpack are well settled and strong.

Problems

Storm Slabs

Another pulse of snowfall and wind will form touchy storm slabs in the mountains over Thursday night and Friday morning. These will be stacking above touchy wind slabs that have yet to fully heal to the surface as well as deeper persistent weaknesses

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Use extra caution in lee areas in the alpine and treeline. Storm snow is forming touchy slabs.Minimize overhead exposure during periods of heavy loading from new snow, wind.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 2

Persistent Slabs

Up to a metre of snow from the past week is bonding poorly to a buried persistent weak layer. The likelihood of triggering a deeply buried weakness will be increasing while new snow and wind add load to the snowpack.

Be aware of the potential for large avalanches due to the presence of deeply buried weak layers.Use conservative route selection, choose moderate angled and supported terrain with low consequence.If triggered, storm slabs may step down to deeper layers resulting in very large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Mar 10th, 2017 2:00PM