Avalanche Forecast

Moderate - Forecast snowfall amounts are uncertain.

Tuesday night: Mostly cloudy with snowfall bringing 15-25 cm of new snow. Moderate southwest winds, becoming strong at ridgetop.

Wednesday: Cloudy with flurries bringing 5-10 cm of new snow and new snow totals to 20-35 cm, continuing overnight. Moderate northwest winds. Alpine high temperatures around -5.

Thursday: A mix of sun and cloud with isolated flurries and a trace of new snow with 2-day snow totals of 25-40 cm. Flurries easing and then beginning again in the evening. Light west winds. Alpine high temperatures around -10.

Friday: Cloudy with continuing flurries bringing 5-10 cm of new snow, totaling up to 15 cm with overnight accumulations. Light to moderate southwest winds, becoming strong at ridgetop. Alpine high temperatures around -4

Recent avalanche activity in the Purcells has been 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 all aspects in alpine terrain. 

A couple of recent MIN reports describe a very large (size 3) deep persistent slab on a well-trafficked slope remote triggered by one or more snowmobiles in the Lang Creek area on Sunday. An adjacent second avalanche may have been triggered sympathetically by the first. On Monday another large (size 2) deep persistent slab was observed just below Gorman Lake. Its trigger is unknown.

As evidenced above, reports from the public as well as explosives control missions continue to demonstrate our snowpack's weakness and ability to produce large, deep avalanches.

Common characteristics of recent avalanches in the region include wide propagation, remote triggers and full depth avalanches scouring away the snowpack to ground.

Earlier last week, there were several instances of large natural events taking out old timber beyond historical avalanche boundaries and running from the high alpine all the way to valley bottom.

Light new snow amounts have begun to bury surfaces over the region that mainly consist of widespread surface hoar ranging from 5-20mm in size. Sun crusts were also observed on steep south aspects in advance of the snowfall.

The Purcells received 60-120 cm of snow from the big storm two weekends ago. This snow has since settled into a slab over a couple of buried surface hoar layers 70-180 cm below the surface. These layers are expected to be progressively gaining strength, but the character of the lower snowpack complicates matters.

The base of the snowpack in the Purcells is astonishingly weak, much weaker than in an average season. This weakness is widespread across aspects and elevation bands, meaning it's almost everywhere. This basal layer consists of crust, facets and depth hoar. 

With the addition of the new snow last weekend, this weakness became overloaded and its failure has resulted in some spectacularly large and destructive avalanche activity. 

• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
• Stick to simple terrain and be aware of what is above you at all times.
• Very large and destructive avalanches could reach valley bottom.
• Stick to simple terrain features and be certain your location isn't threatened by overhead hazard.