Purcells

We have entered a low probability/high consequence period. Large and destructive human-triggered persistent slab avalanches remain possible.

Fair - Timing, track, or intensity of incoming weather system is uncertain

The ridge of high pressure shifts into Alberta allowing a weak cold front to reach the interior Thursday overnight. Thursday should see a mix of sun and cloud up high with a layer of valley fog in most of the valleys. Alpine winds should remain light and freezing levels are expected to reach around 700m. Thursday night and Friday are forecast to receive 3-6mm of precipitation with moderate-to-strong SW alpine winds. Freezing levels are expected to be around 1500m. By Friday evening the system should be finished. Saturday is expected to see a mix of sun and cloud, freezing levels around 800m, light alpine winds, and the possibility of light flurries. Another weak system is expected for Sunday.

Explosive control on Tuesday produced two size 2 slab avalanches in the deeper western part of the region.  These avalanches released on the mid-Dec layer down 90-100cm on steep north aspect slopes.  No new avalanches were reported on Sunday or Monday. Natural avalanche activity is not expected on Thursday. Skier triggering a persistent slab avalanche remains the main concern for the foreseeable future.

A layer of surface hoar up to 10mm sits on the snow surface. A sun crust exists on steep sun exposed slopes. In the alpine, wind affected surfaces are expected.  Recent warm temperatures have aided in the settlement of the week old storm snow. The persistent slab is typically 40-80cm thick and sits on the mid-December surface hoar/crust layers which remains sensitive to human triggering. The reactivity of this persistent weak layer appears to be quite variable but still has the potential for large, destructive avalanches in some areas. The layer appears to be the most reactive at treeline or just below treeline. The mid-Nov weak layer is near the bottom of the snowpack but has become inactive.