Progressive storm loading and a buried weak layer have created tricky conditions. Watch for fresh wind slabs on Thursday and use extra caution on south facing slopes when the sun is out. Conservative terrain selection remains critical.
Summary
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Mainly cloudy conditions are expected on Thursday with light snow flurries and sunny breaks both possible. Alpine wind is expected to be moderate from the southwest and treeline temperatures are forecast to reach around -6C. A storm system is expected to reach the region Thursday evening. 20-30 cm of snow is forecast between Thursday evening and Friday afternoon. Alpine wind is forecast to be strong from the southwest and treeline temperatures are forecast to reach around -3C. The next storm system is currently forecast to arrive on Saturday afternoon or evening.
Avalanche Summary
On Tuesday, skiers and explosives were triggering size 1 wind slabs which were up to 30 cm thick. Natural sluffing from steep terrain features was also observed. On Monday, two natural size 1 wind slabs were observed on a southwest aspect in cross loaded terrain which were 20 cm thick. A skier triggered a size 1 storm slab on an east aspect at 1800 m and explosives triggered three size 1.5 storm slabs which were 15-20 cm think. On Thursday, large persistent slab avalanches remain a concern for the accumulated snow from the past week releasing on the February weak layers. It may still be possible for a person to directly trigger a persistent slab or a smaller avalanche could step down. Recent strong southwest wind has created new wind slabs in immediately leeward terrain features which are expected to remain touchy on Thursday.
Snowpack Summary
Moderate to strong southwest wind Tuesday night redistributed the most recent storm snow forming new wind slabs in leeward terrain at higher elevations. Another 10-15 cm on Tuesday brings the typical storm accumulation in the past week to 60-100 cm. This snow has settled into a slab that sits over the mid-February weak layer which consists of facets and/or surface hoar overlying a thick crust. In wind loaded terrain, this layer may be down 150 cm or more. Recent observations suggest this layer is still reactive and capable of producing wide propagations if triggered. We have been in an incremental loading scenario over the past week and this layer has not yet been fully tested. Expect it to wake up during the storm on Friday. Below the crust layer, the mid and lower snowpack are well settled and strong.
rbuhler,
Avalanche Canada
