Purcells

Poor - Freezing levels are uncertain

The ridge of high pressure is forecast to continue to bring clear skies to the region on Sunday night and Monday. There is a temperature inversion forecast to move into the area from the Northwest. This means that it may be warmer in the Alpine than it is in the valley. This condition should be fairly short lived on Monday, and then replaced with below freezing temperatures down to the valleys by Tuesday morning. Strong South-westerly winds are forecast for Tuesday morning as a fast moving cold front move through the region. The ridge of high pressure should re-build on Wednesday, and there may be another period of above freezing temperatures in the alpine.

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.