Purcells

Tricky avalanche conditions require extensive experience to travel safely at and above treeline this weekend.

Fair - Due to limited field observations

The weekend brings, cool, dry, mainly sunny conditions as a ridge of high pressure remains over the region. Ridgetop winds from the northwest will be near 40km/h. Alpine temperatures steady at -7, with freezing levels rising to 600m then dropping back to valley bottom. On Monday we may see milder conditions, and a westerly flow ahead of the next approaching cold front.

Control work done on Tuesday produced a size 2 avalanche running to ground from a northeast aspect. There is still very limited observations from the region, so you will have to do the detective work. I suspect these conditions will continue through the forecast period, and it's likely that avalanches are susceptible to human/ sled triggering. With clear skies ahead this is a good opportunity to make snowpack, and avalanche observations from your surrounding mountains before jumping in to deep. I bet you'll be able to see evidence of older, large avalanches that occurred on your local mountains. I do suspect that these slopes will be ripe for human, and/or sled triggering especially on northerly aspects where avalanche activity has not occurred. Remember these avalanches are failing on weak facetted (sugary) snow at the bottom of the snowpack, producing full depth avalanches.

Snow depths are quite variable through the region. In the alpine there is 170- 250cm. At treeline there is anywhere from 130-150cm. Sunday's warm, moist storm combined with strong southwesterly winds created stiff wind slabs on north-east slopes. Changing winds through the weekend at ridgetop and treeline will redistribute snow, forming new wind slabs on southerly aspects. The upper snowpack is tightening up forming a stronger mid-pack. A highlighted concern for the Purcells was the mid-November storms that created a heavy slab over a weak basal faceted base. The Purcells saw a significant cycle of large avalanches running full depth as a result. (The Lizard Range also saw very similar results all failing on the weak basal layers.) Conditions are ripe for human triggered avalanches, starting as a wind slab that could step down to weak basal facets (sugary snow) producing large destructive avalanches with high consequence.