Purcells

Poor - Timing, track, or intensity of incoming weather is uncertain

The next wave of snow is forecast to move into the interior from the coast on Saturday afternoon. The freezing level should rise quickly up to about 2000 metres late in the day Saturday, descend a bit overnight into Sunday and then rise again Sunday to about 2000 metres. This storm is forecast to bring strong southwest winds and moderate to heavy precipitation from Saturday afternoon until late in the day Sunday. Monday should be much drier and cooler as high pressure moves in behind the storm. I think that this storm will probably cause another cycle of natural avalanches, and continue to cause conditions that are very likely for human triggering.

Natural and helicopter explosive control work in the Purcells produced very large avalanches up to size 3.5 with wide propagations and fast moving slides that ran further than expected. We had a report today from a professional member that flew through the Selkirks south of Revelstoke on Thursday. Widespread natural activity was observed up to size 3.5 in the alpine that was running full path into the valleys. Some fracture lines appeared to be about 2 metres deep and very wide. In some areas very large avalanches had run out onto low angle terrain. Most avalanches had initiated between 2200m and 2600m. Avalanches were observed from all aspects, with north and east being the most frequent. I think that there is a great deal of variability out there, and we should all be very conservative this weekend.

Generally we have about 150 cms in the alpine, and treeline has been showing some variability between 50 -150 cms. There are locations in the alpine that have 200 cms plus already. The freezing level went up to about 1900 metres on Wednesday and caused some pretty rapid settlement, followed by below freezing temperatures that have re-frozen the snow pack up to about treeline elevations. The wind has come from the southwest during the last storm, and then strong from the northeast immediately following the storm. Yesterday the wind was strong in the alpine from the east-southeast. We were feeling pretty sure that there was a major avalanche cycle going on in the alpine, that we thought was probably failing on the buried surface hoar layer that has been reported to be down about a metre. Today we received new information from the Selkirks south of Revelstoke that there was indeed a major avalanche cycle up to size 3.5 during the last storm, but it appears that most of the avalanches were sliding on a layer that is near the ground; perhaps a rain crust from October. The slides may have started on the surface hoar layer and then stepped down to the crust. We hope to get some more information soon, as operators start getting out into the field. There is probably a lull in activity today (Friday), but I am hesitant to bring down danger ratings with the limited information that we have. The next storm is forecast for Saturday, and it looks like it is going to come in warm again, maybe up to 2000 metres. I think the "take home" advice from recent activity is that you should be very suspicious of any slopes in the alpine that have not recently avalanched. If there is a crust of some type down low near the ground, you should be watching out for areas that might re-load with the next storm. Due to the variability of the amounts of snow in different drainages, I think that the absence of recent avalanche activity in an area would concern me as well. These are difficult early season conditions to evaluate. I recommend being very conservative this weekend. It is going to take a few days at least before we see any improvement. Let me know what you think! [email protected]