Avalanche Forecast

Friday night: Scattered cloud, alpine low -16 C, alpine wind moderate northwest.

Saturday: Scattered cloud, alpine high -9 C, alpine wind light to moderate northwest.

Sunday: Scattered cloud, alpine high -7 C light northeast wind.

Monday: Scattered cloud, alpine high -6 C, light northwest wind.

Avalanche activity in the Purcells this week is simultaneously impressive and terrifying. Explosive control work in the central portion of the region continues to produce large persistent slab avalanches size 3 and larger on north and east facing alpine terrain. Common characteristics include wide propagation, remote triggers and full depth avalanches running to ground.

On Wednesday a group of skiers remote triggered a size 3 deep persistent slab avalanche in the Golden backcountry. The avalanche occurred on a southwest through northwest facing terrain feature in the alpine. The crown was up to 1 m deep. The same group also observed numerous large avalanches that failed naturally and went to ground. Earlier in the week, there were several instances of large events taking out old timber beyond historical avalanche boundaries and running from the high alpine all the way to valley bottom.

The Purcells received 60-120 cm from last weekend's big storm which has been settling into a slab over a couple of buried surface hoar layers 70-180 cm below the surface. This is normally a recipe for a concerning persistent slab avalanche problem in its own right, but there's more to the story...

The base of the snowpack is astonishingly weak, far more so than in the average season. This weakness is widespread across aspects and elevation bands meaning it's almost everywhere. It consists of crust, facets and depth hoar. With the addition of the new snow last weekend, the weakness became overloaded and its failure has resulted in some spectacularly large and destructive avalanches recently.

• Conservative terrain selection is critical, choose only well supported, low consequence lines.
• Stick to simple terrain or small features with limited consequence.
• Don't let the desire for deep powder pull you into high consequence terrain.
• Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.