Avalanche Forecast
Issued: Feb 15th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
astclair,
Avalanche Canada
Watch for wind slabs in unusual places. These slabs have potential to break wider than expected and may be slow to bond. Read about managing these conditions in this forecaster blog.
Summary
Confidence
Weather Forecast
MONDAY NIGHT: Mostly cloudy, light flurries with a trace of snow, moderate west wind at ridgetop, alpine temperatures around -13 C.
TUESDAY: Cloudy, light flurries with a trace of snow, moderate west wind with strong gusts at ridgetop, alpine temperatures around -13 C.
WEDNESDAY: Cloudy, light flurries with a trace of snow, moderate southwest wind, alpine temperatures around -12 C.
THURSDAY: Increasing cloud, strong south winds, alpine high temperatures around -8 C.
Avalanche Summary
On Saturday, observers near Valemount reported small loose dry sluffs on steep terrain in the trees (MIN report).
On Thursday, a MIN report in the south of the region detailed a spike in wind speed and a shift in direction to northeast that formed touchy slabs, loaded cornices to their breaking point, and likely initiated a large avalanche in the alpine. A MIN report on Saturday indicated that a similar pattern of wind slab and cornice activity had previously occurred in areas around Valemount .
Earlier in February, there was widespread avalanche activity on a weak layer of buried surface hoar, mostly on treeline features (see some photos in the MIN reports here, here, and here).
Snowpack Summary
Winds have varied in strength and direction over the past week, loading cornices and forming wind slabs at upper elevations that may still be possible to trigger. Watch for these wind slabs in unusual places as complicated cross-loading and reverse-loading patterns are prevalent. Wind slabs may overlie weak, sugary, faceted snow, meaning that they could break wider than expected and will likely be slow to bond.
In wind-sheltered areas, the upper snowpack has become soft and faceted from the cold temperatures. 40-70 cm of snow from February is settling over a reactive weak layer of surface hoar buried in late January. Reactivity on this layer has primarily been observed at treeline and in "treeline-like" features, like cutblocks, that are below treeline. Snowpack test results continue to show instability on this layer, like this MIN report from Allan Creek on Friday. On steep south-facing terrain, this layer may consist of facets on a sun crust.
Additional weak layers may present in the lower snowpack, but are not a concern in most areas until we see significant snow loading or rapid warming.
Terrain and Travel
- Recent wind has varied in direction so watch for wind slabs on all aspects.
- Approach lee and cross-loaded slopes with caution.
- Be aware of the potential for large avalanches due to the presence of buried surface hoar.
- Extra caution is needed around cornices under the current conditions.
Problems
Wind Slabs
Shifting winds from all compass directions in the past week have formed a complex pattern of wind slabs at upper elevations that may be possible to trigger. Given the potential for cross-loading and reverse-loading, treat all aspects as suspect. Cornices may be reaching their breaking point.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A weak layer of surface hoar is buried 40-70 cm deep that may be possible to human trigger. This layer has been most sensitive around treeline, but may also extend into alpine terrain and/or down into the trees.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 16th, 2021 4:00PM
