Backcountry Advisory 

As of Wednesday, Dec. 12 th

The Westerly flow that has continued to dominate our weather patterns has provided us with another week of excellent backcountry skiing conditions. Since last week’s advisory, we have received an additional 74cm. of new snow at the 1650m elevation on Whistler Mountain.

Storm snow instabilities generally dominated the big picture this week, with widespread natural activity occurring during the height of the storm-cycle last Saturday. A cooling trend followed the storm, and rapid settlement and sintering quickly tightened up the storm-snow layers. Explosive control and ski testing on Sunday resulted in predominantly shallow surface releases from 10-25cm in depth. Of note were several large anomalous releases that went down to the November crust and facet layers mentioned in previous advisories. A size 3.0 avalanche was triggered during heli-bombing last Sunday on Whistler Mountain. The crown line maxed out at close to 2m in depth. This slide was triggered by a medium sized cornice falling onto the sweet spot of the start zone, where the crust was buried shallow and the overlying faceted layer was quite well developed. It pulled out the whole width of the slope, which was one solid cohesive mass of predominantly pencil to knife layers underlying the storm-snow. Several releases on Blackcomb Mountain were also suspected to have run on this layer. In these cases the start zones were steep unsupported convex rolls.

Another layer of surface hoar formed yesterday and overnight. In one area below the treeline this morning it had already grown as large as 10mm. in size. This layer could become reactive once it receives sufficient loading, particularly in some rather innocuous creek beds and terrain traps at and below the treeline.

Yesterday a large cornice fall was triggered in an area adjacent to the ski area boundaries. The trigger was a skier who ventured out towards the edge to get a better view. The view ended up being a bit more than he bargained for when all of a sudden the cornice gave way and there was nothing but air under his toe-pieces.

He learned a valuable lesson in this instance.

If you are ever involved in or witness an avalanche inside or outside the ski area boundaries, please contact the ski patrol even if there was no one involved. This way we can prevent many of the unnecessary SAR responses that occur each year.

The forecast is calling for a continued cool Westerly flow for the next several days, becoming more Northwesterly and cooling further on Friday and Saturday. The first wave that began this morning will bring moderate snowfall accumulations. The main energy of the second wave that is approaching appears to be heading to our South. We may see nothing more than flurries out of that one. If the long-range computer models pan out, by Sunday we will be into more of a Southwesterly flow with milder temperatures and heavy snowfall accumulations.

The Backcountry Avalanche Danger in the areas adjacent to Whistler/Blackcomb is Currently rated as MODERATE, but may rapidly increase with continued snowfall and wind-loading.

Conditions may vary and can change rapidly. Check with the Whistler Blackcomb Advisory phone line at 604-938-7676 for the current conditions in areas adjacent to Whistler and Blackcomb Mountains. If you area venturing further afield, or for other areas in the province check the CAA Web site at www.avalanche.ca for the Public Avalanche Bulletin, or call 1-800-667-1105.

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