Avalanche Forecast
Issued: Jan 13th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Persistent Slabs and Loose Wet.
swerner,
Avalanche Canada
Don't let the sunshine and fresh snow lure you into aggressive terrain. Storm and wind slabs will likely remain reactive to rider triggers, especially where they sit above a persistent weak layer. Use a conservative approach and be aware of overhead hazards like cornices.
Summary
Confidence
Weather Forecast
An upper ridge will build Thursday bringing dryer and sunnier weather.
Thursday/ Friday: A mix of sun and cloud. Alpine temperatures near -2 and freezing levels 1200 m. Ridgetop wind light-moderate from the southwest.
Saturday: Cloudy with some flurries. Light West wind and freezing levels 800 m.
Avalanche Summary
On Wednesday, a widespread natural avalanche cycle up to size 2.5 was reported on all aspects and elevations. A recent MIN report observed from Rossland also shows a size 3 natural persistent slab avalanche that occurred during or post-storm.
On Tuesday, explosive control triggered numerous size 2-2.5 slab avalanches and human triggered avalanches up to size 1.5 were also reported.
Natural and human triggered slab avalanches will continue to exist on Thursday.
Of note, a naturally-triggered size 3 deep persistent slab avalanche released on a southeast aspect at 2200 m in the Rossland range last Tuesday or Wednesday. The avalanche likely failed on the weak layers described in the Snowpack Summary and scrubbed to the ground.
Snowpack Summary
Up to 40 cm of recent storm snow accompanied by strong to extreme westerly wind has built reactive storm and wind slabs at upper elevations. These slabs may be extra sensitive where they overlie surface hoar in sheltered terrain. Warmer temperatures and a period of rain overnight Tuesday has formed a 3mm surface crust to 1780 m in Kootenay Pass.
Two weak layers are buried in close proximity to one another. They are 70 to 130 cm deep. The layers are composed of surface hoar and faceted grains and they overlie a hard melt-freeze crust. This recent MIN report observed from Rossland on Wednesday the 13th shows good evidence of a large natural slab avalanche failing on the early December persistent layer during or post-storm. This suggests that it remains possible for riders to trigger these layers.
Another layer of faceted grains above a melt-freeze crust that formed in early November is upwards of 200 cm below the surface. This has been the suspected failure layer of a few very large avalanches that released last week in the Rossland range.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
- Cornice failure may trigger large avalanches.
Problems
Storm Slabs
Up to 40 cm of recent storm snow blanketed the region. Strong to extreme ridgetop wind came with the storm building reactive storm and wind slabs at upper elevations.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Weak surface hoar and/or faceted grains sit above a melt-freeze crust around 80 to 130 cm deep. The likelihood of triggering a persistent slab has reduced, but the consequence of doing so remains high.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Loose Wet
Sunshine and rising freezing levels may trigger loose wet avalanches, especially in steep terrain features and from solar aspects.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Jan 14th, 2021 4:00PM
