Backcountry Advisory As of Feb.23rd, 2000 Mountaintop winds were gusting to 160 km/h. at the Peak of Whistler Mountain on Tuesday. They were initially from the Southeast, switching to the Southwest later in the day. Any windward slopes were literally pounded by the winds, with some trees snapping like match sticks. Approximately 20 cm. of new snow has fallen during the past 24hours. The 5cm of new snow which fell overnight was accompanied by cooler temperatures. This cooling trend appears to have significantly tightened up the shears within the storm-snow layers. This morning an easy shear was observed at the new snow interface. The only significant results with avalanche control this morning were restricted to the immediate lee of some terrain features low in the start zone on some NW facing slopes. Some good sized cornice releases were also observed to have occurred. The storm snow layers can be found to be resting on a variety of old surface features. You may all recall that surface hoar has continued to grow periodically during the past week. There was also a layer of light density snow on North and North East facing slopes that had undergone some faceting while alpine temperatures hovered in the –15.0 º C. range. On some slopes a one finger to pencil resistant wind-slab was resting above these layers, while on others it was resting on a melt-freeze crust. So now you can add to this potpourri our most recent wind-slab, which on some slopes in the alpine will be resting directly on the aforementioned melt-freeze crust. High velocity winds quite frequently have a tendency to form a very stiff or hard slab. The lack of penetration of a skier or snowboarder through the surface of these slabs might tend to lull the somewhat less-experienced backcountry enthusiasts into a false sense of security. Be wary of any slopes that have a hollow feel to them. The overlying slab may initially be strong enough to support the weight of a person. However, one might find that approaching a weaker point in the slope (such as a rock outcropping or the thin part of the slab) might result in a failure from within that can propagate across the entire slope. Hard slabs fail initially as one solid mass. As they begin to descend the slope the speed increases and they begin to break up into smaller pieces that pile up on one another as the avalanche comes to a halt. They are nasty things that one would be prudent to avoid! Cornices have been observed to be calving large chunks recently, some of which were large enough to turn a vehicle into a piece of scrap metal. I’ll leave it to your imagination the effect it would have when coming in contact with a skier or boarder. The backcountry avalanche danger is rated as CONSIDERABLE, trending to MODERATE. Remember that conditions may vary and can change rapidly. Call the CAA Public Bulletin @ 1-800-667-1105 for more info, or locally call 938-7676.
