Purcells

The storm is forecast to continue overnight. New snow, wind, and warming temperatures are keeping the avalanche danger HIGH.

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

Pacific moisture is forecast to move into the North interior today and then slide down the West side of the Rockies as it is deflected by cold arctic air over the prairies. This next pulse of moisture starting Monday afternoon is expected to bring 10-20 cm of new snow to the West of the region, and 5-10 cm of new snow to the East of the region. Areas with higher snowfall should have stronger Westerly winds, and areas with lighter snowfall should have lighter Northwest winds. Western and Southern areas may have freezing levels up to 2200 metres, and Eastern and Northern areas may see freezing levels rise up to about 1400 metres. There is a chance of above freezing air becoming trapped in the alpine as the warm Pacific moisture rides up over the colder arctic air. The storm snow should end by Wednesday morning, but strong Northwest winds and locally high freezing levels are expected to continue during the day. A ridge of High pressure should build on Thursday bringing clearing skies, cooler air, and light Easterly winds.

Skier triggered and explosives triggered avalanches were reported up to size 2.0 that were about 40 cm deep. I suspect that avalanche activity will increase with the next pulse of moisture overnight, and natural avalanches may release during the storm.

A new storm storm slab has started to develop above the recent isolated pockets of touchy windslab in the alpine and at treeline. Since previous winds were from the north or northwest, wind slabs should be suspected on a wide variety of aspects in exposed terrain. A thin layer of surface hoar with variable distribution was buried on December 27th by about 5-10 cm of light dry snow. As more snow accumulates, this interface could become one to watch. Deeper, at about 40-60 cm below the surface, a persistent crust/surface hoar layer from mid-December can be found. This persistent slab problem is reasonably widespread across the region and is not expected to improve quickly. A deeper crust/facet layer which formed early in the season may still be triggerable from thin or rocky snowpack areas.