Purcells

New wind slabs are just the latest in a list of avalanche problems plaguing the region. Avoiding triggering one will be the first step in avoiding deeper persistent weaknesses.

Moderate - Forecast snowfall amounts are uncertain

Thursday night: Increasing cloud with isolated flurries and a trace of new snow. Light southwest winds, increasing to strong in the alpine.Friday: Cloudy with scattered flurries bringing 5-10 cm of new snow, continuing overnight. Light southwest winds, increasing to strong or extreme in the alpine. Alpine high temperatures around -4.Saturday: Mainly cloudy with easing flurries bringing a trace of new snow, with new snow totals to 10-20 cm. Another round of light flurries beginning overnight. Light to moderate southwest winds easing over the day. Alpine high temperatures around -6.Sunday: Cloudy with scattered flurries bringing up to 5 cm of new snow, with new snow totals to 15-30 cm. Light southeast winds. Alpine high temperatures around -15 and dropping over the day.

On Tuesday a skier triggered a small storm slab on a very steep east facing feature around 2100 m. A size 2 wind slab was triggered when ice fall impacted a north facing slope at 2600 m.On Monday a natural size 2.5 wind slab avalanche was observed on a steep south facing feature at ridgecrest (2700 m). The wind slab had a crown 60 cm in depth. A cornice failure produced a size 3.5 deep persistent slab on a northeast facing slope at 3000 m that ran for 2 km. The crown was reported to be up to 300 cm in depth which suggests it failed on the late October weak layer at the very bottom of the snowpack. There's a great MIN report from Monday of a deep persistent slab that failed naturally on a SW facing feature at treeline.There is a great MIN report from January 22nd that shows a natural avalanche (size 3.5) in International Basin, also on the deep persistent layer. Check it out here.

The current surface is a mix of sastrugi, old wind slab, facets, sun crust and a bit of surface hoar. Last weekend was warm & extreme wind came out of the south, southwest and northwest. This left a robust crust (up to 4 cm thick) on steep south facing aspects and redistributed snow into wind slabs which have grown old and tired. The warmth allowed 10 to 35 cm of snow to settle into a slab above the mid-January persistent weak layer (PWL) which is made up of large surface hoar that is most prevalent at and below treeline. On steep solar aspects this interface presents as a crust, there may be locations where the surface hoar actually sits on the crust.The snowpack is harboring a nasty weak layer near the ground composed of weak facets above a crust. This interface continues to produce sporadic avalanches that are very large and destructive. Avalanches triggered on this weak layer take the entire seasons snowpack with it and have resulted in numerous close calls and serious incidents. This layer is most likely to be triggered from zones where the snowpack is thin and weak. Rock outcroppings and ridge crests around large open slopes and bowls in the alpine are particularly suspect