Avalanche Forecast
Issued: Feb 11th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs, Cornices and Wind Slabs.
TRettie,
Avalanche Canada
When in doubt ride simple terrain. The likelihood of triggering avalanches could change rapidly with warming and solar input. There is some uncertainty in where and when slab properties could exist above the late January layer. Use caution at treeline and avoid overhead hazard.
Summary
Confidence
Weather Forecast
Friday night: no new snow expected. Moderate northwest winds in the alpine. Low of -11 at 1700m.
Saturday: sunny with the possibility of a temperature inversion and freezing levels rising to 1500m in the north and 2000m in the south of the range. Light to moderate northwest winds in the alpine.
Sunday: mix of sun and clouds with freezing levels rising to 1500m. Light northwest winds shifting to west in the afternoon.
Monday: light precipitation bringing trace amounts of snow. Light west winds and freezing levels rising to 1200m.
Avalanche Summary
On Thursday loose wet avalanches were observed up to size 1.5 on solar aspects at lower elevations. One size 2 wind slab avalanche was triggered by explosives on a morainal feature at 2200m.
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.
Snowpack Summary
A new melt-freeze crust is expected on solar aspects into the alpine and on all aspects below treeline. This crust will likely break down and become moist as the freezing level rises and the sun comes out. Previous strong wind from the southwest through northwest have formed wind slabs at higher elevations and over hanging cornices on some ridge features.
The January 30 interface is now typically down 20-50cm and consists of a melt-freeze crust 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.
Terrain and Travel
- Minimize exposure to sun-exposed slopes when the solar radiation is strong.
- Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
- Cornices become weak with daytime heating or solar exposure.
- Be careful as you transition into wind affected terrain.
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 earlier in the week. 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 such as a cornice. These layers could become more reactive with higher freezing levels and solar radiation. Warm temperatures could promote slab formation and increase the potential for propagation.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
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, Treeline.
Likelihood
Expected Size
Wind Slabs
Recent strong winds from the SW through NW have formed wind slabs in exposed terrain at higher elevations.
Aspects: North, North East, East, South East, South, South West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 12th, 2022 4:00PM
