Avalanche Forecast

Issued: Mar 11th, 2017 4:57PM

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

Avalanche Canada cgarritty, Avalanche Canada

Ongoing snowfall and wind inputs are sustaining elevated danger in the region. Persistent weaknesses deeper in the snowpack continue to be tested.

Summary

Confidence

Moderate -

Weather Forecast

Saturday night: Flurries bringing 10-15 cm of new snow. Moderate to strong southwest winds. Sunday: Continuing flurries bringing approximately 10 cm of new snow, mainly in the afternoon. Light to moderate southwest winds. Freezing level to 1500 metres with alpine temperatures of -3. Monday: Flurries bringing approximately 10 cm of new snow, mainly in the afternoon. Rain below about 1400 metres. Light to moderate southwest winds. Freezing level to 1800 metres with alpine temperatures around 0. Tuesday: Flurries bringing approximately 10 cm of new snow to higher elevations, intensifying overnight. Rain below about 1600 metres. Moderate to strong south winds. Freezing level to 2000 metres with alpine temperatures around 0.

Avalanche Summary

Reports from Friday include extensive results of explosives control in the Whistler area, with numerous storm slabs, cornices, and wind slabs releasing from Size 1.5-2. Another highly notable report from southwest of Whistler details a remotely triggered Size 1.5 persistent slab. This avalanche released from a northeast aspect, had a crown fracture depth of about a metre, and should highlight ongoing concern for lingering weakness at our mid-February layer.Looking forward to Sunday, expect recently formed storm slabs to remain reactive to human triggers. While the bond at mid-February interface remains questionable, the possibility of large persistent slab avalanches also remains a concern.

Snowpack Summary

Stormy weather over the past week has brought 80-130 cm of recent snow to the region. Moderate to extreme southwest to southeast winds have redistributed much of this storm snow over the same time period and formed touchy new storm slabs in lee terrain at higher elevations. The combination of wind and warming temperatures has seen the storm snow settle into a slab that sits over the mid-February weak layer. This layer consists of facets and/or surface hoar overlying a thick crust. In wind loaded terrain, this layer may be down 180 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 where as this layer gradually heals, it is continually tested as new snow and wind load the snowpack. Below the crust layer, the mid and lower snowpack are well settled and strong.

Problems

Storm Slabs

An icon showing Storm Slabs
Another pulse of snowfall, wind, and warm temperatures on Sunday will contribute to an already touchy storm slab problem. These fresh storm slabs are stacking above deeper persistent weaknesses that still can't be trusted.
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 will have formed touchy slabs.Be increasingly cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing 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 12th, 2017 3:00PM

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