Avalanche Forecast
Regions: Purcells.
VKeep an eye on daytime warming and solar input. There is uncertainty in freezing levels and how the snowpack will react. Avoid overhead hazard.
Confidence
Low - Uncertainty is due to difficult to forecast freezing levels.
Weather Forecast
Wednesday night: possibility of light rain. Freezing levels staying around 2200m. Moderate to strong west winds in the alpine.
Thursday: Mainly sunny with light to moderate northwest wind. Freezing levels in the morning around 2500m and gradually falling throughout the day.
Friday: sunny with Freezing levels around 1600m . Light northwest winds.
Saturday: Mostly sunny with a high of -2 at 1700m. Light northwest winds.
Avalanche Summary
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.
On Sunday, several natural wind slabs and loose avalanches were reported. A skier remotely triggered a size 1.5 wind slab from 3 m away on an east aspect at 2500 m. Explosives triggered a number of slab avalanches size 1.5-2.5 in the deeper west part of the region where the slab thickness was typically 30-50 cm and up to 120 cm in wind loaded terrain.Â
This MIN post from the Dogtooth shows the type of open slopes where the buried surface hoar may be reactive at lower elevations.
Snowpack Summary
With high freezing levels and sunny skies moist snow will likely be observed on all aspects at and below treeline as well as south facing slopes in the alpine.
Previous strong wind from the southwest through northwest have formed wind slabs in exposed terrain at higher elevations.Â
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 40-90cm deep. Â
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.Â
Terrain and Travel
- Be aware of the potential for large avalanches due to the presence of buried weak layers.
- Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
- Back off slopes as the surface becomes moist or wet with rising temperatures.
- Avoid exposure to slopes that have cornices overhead.
- Be careful as you transition into wind affected terrain.
Avalanche Problems
Persistent Slabs
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. This layer could become more reactive with higher freezing levels and solar radiation.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood: Likely
Expected Size: 1.5 - 2.5
Cornices
Large overhanging cornices have formed. Avoid travel underneath these hazards. cornice falls can trigger slab avalanches on the slopes below.
Aspects: North, North East, East, South East, South.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1.5 - 2.5
Wind Slabs
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.
Aspects: North, North East, East, South East, South, South West, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2