Backcountry Advisory When forecasting avalanches, whether for a ski tour or for a commercial operation, there are three types of information from which to draw. The most relevant is referred to as "type one data," or observed avalanche activity. Type two and three data are less direct sources of information such as weather conditions and trends, snowpack history, slope history, etc. When the frequency and magnitude of avalanche activity contradicts the expectations of the decision maker it is time to re-evaluate the data. The avalanche activity of the past week (from Dec. 1 onward), and especially on Dec. 5 is indicating that here on the coast it is re-evaluation time. A rain crust that formed on Nov. 17, 1999 (remember this one) is the main problem. November 17 was the last day of an extended warm, wet precipitation event that saw the snow line fall to 1,500 metres leaving a thin blanket of new snow over the otherwise rain-soaked snowpack. While the wet snow froze the new snow faceted. Now this weak interface is sliding. The snow pack over the November crust has been gradually increasing, and releasing with some predictability. We have been tracking the weakness and thought we had a good grasp of where it was likely to release, repeatedly testing it and thinking we had it in some degree of control. Now I think we were wrong. Skiers have been taking advantage of the current Ski Area Boundary status of the remaining lift accessible avalanche terrain around the Whistler/Blackcomb ski area. Many are skiing alone, without rescue gear, and without caution in terrain that is plainly marked as uncontrolled, or at best marginally tested. We witnessed some skiers blindly shred into Diamond Bowl without noticing the 1.5 metre crownline triggered that morning, and fall onto a blue ice bedsurface. What if the slope had not slid in the morning? What if they had triggered it? It ran almost all the way to the valley bottom. The only reason it didn't was because of the large boulders in the lower bowl that slowed it down. This is unwise behaviour. Since Dec. 1 we have seen almost daily avalanche activity of size 2.5 to size 3 magnitude from previously tested and, possibly more significantly, previously skied and boarded terrain. To state this more plainly, large slopes are releasing on the Nov. 17 weakness with crowns of 0.5 to 2+ metres. They are fracturing high in the start zones, across the whole slope, and are running far. Worst of all, these avalanches are being triggered by seemingly minor stresses, after previous testing with large explosives. The windroll of Blackcomb Glacier released on Dec. 05 sympathetically to an explosive trigger on a higher target that released only a size 1 avalanche. I had skied the glacier the previous day. The crown was two meters deep and ran "wall to wall." This is an average 30 degree slope that is well supported and runs only very rarely. The slopes above had run as large size 2s on at least two occasions over the previous week. Clearly the hazard in the snowpack at this time is significant. Check with the local ski patrols for up to date information on the latest hazard ratings, or call the Canadian Avalanche Association at 1-800-667-1105.
