When in doubt choose simple terrain. The likelihood of triggering avalanches can change rapidly with rising freezing levels and solar input. Use extra caution at treeline and on slopes with overhead hazard.
Recent strong winds from the SW through NW have formed wind slabs in exposed terrain at higher elevations. These slabs are particularly reactive where they overlie buried surface hoar.
Large overhanging cornices have formed. Avoid travel underneath these hazards. cornice falls can trigger slab avalanches on the slopes below.
20-50cm of settling snow sits over the January 30 surface hoar crust layer. This layer was responsible for several natural and human-triggered avalanches over the past week. Treat open slopes at and below treeline with extra caution. The mid January crust/facet layer is down 40 to 120 and could be triggered in shallow snow pack areas or by a large load. These layers could become more reactive with higher freezing levels and solar radiation.
Thursday night: no new snow expected. Moderate northwest winds and freezing levels falling to near valley bottom.
Friday: sunny with Freezing levels around 1600m . Light to moderate northwest winds.
Saturday: sunny with freezing levels rising to 1500m and the possibility of a temperature inversion. Light northwest winds.
Sunday: Mostly sunny with freezing levels rising to 1500m. Light northwest winds shifting to west in the afternoon.
On Wednesday in the southern part of the forecast region a skier triggered a size 2 wind slab avalanche in a steep rocky feature at 2600m on a east aspect. This avalanche ran on the mid January crust.
On Tuesday several small cornice falls were observed triggering slab avalanches up to size 2 in lee and cross loaded features at treeline and above. A skier triggered a size 1.5 slab avalanche on a steep treeline feature on a south aspect, this avalanche ran on the late January layer.
This MIN post from the Dogtooth shows the type of open slopes where the buried surface hoar may be reactive at lower elevations.
We expected a new crust at and below treeline on all aspects. This crust will likely soften at lower elevations and on sun exposed slopes during the day.
Strong westerly winds have formed wind slabs in exposed terrain at higher elevations and scoured windward slopes.
The January 30 interface is now typically down 20-50cm and consists of a melt-freeze crust at lower elevations and on solar aspects extending into the alpine, surface hoar in sheltered areas at and below treeline, and small facets in some areas.
Several old surface hoar layers are now buried in the upper snowpack 40-120cm deep.
The early December crust/facet layer of concern sits around 80 cm deep in the eastern Purcells and shallow terrain, and up to 150 cm in the west. This layer produced numerous large avalanches in January but is now considered dormant. See this forecaster blog on how to manage this layer as it may come into play again later this season.
