Avalanche Forecast
Issued: Mar 17th, 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.
JSmith,
Avalanche Canada
Southwesterly winds continue to form wind slabs on lee and cross-loaded terrain features in the alpine. Use caution when transitioning into wind affected terrain and avoid wind loaded slopes below ridgetops.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
 Â
WEDNESDAY NIGHT: Clear / Strong, southwest ridgetop wind / alpine low temperature -9 / Freezing level valley bottom.
THURSDAY: Increasing cloud in PM, then 5-10 cm. overnight / Strong, southwest ridgetop wind / alpine high temperature 0 / Freezing level 1900 m.
FRIDAY: Mix of sun and cloud / Strong, southwest ridgetop wind / alpine high temperature -2 / Freezing level 1500 m.
SATURDAY: Mix of sun and cloud / Moderate, northwest ridgetop wind / alpine high temperature -9 / Freezing level 800 m.
Avalanche Summary
A few naturally triggered size 2 wind slabs on northerly aspects in the alpine were reported on Tuesday.
Our field team found some large and disturbingly wide avalanches in the Hasler last week, with lots of compelling images in their MIN report here. It's suspected that these are running on facets that are about 80 cm below the surface.
Snowpack Summary
The northern portion of the region around Pine Pass got around 35 cm. of snow last weekend, but much less fell in the rest of the region. Southwesterly winds have formed wind slabs on lee and cross-loaded features below alpine ridgetops.Â
Sun crust exists on solar aspects and a temperature crust may exist on all aspects up to 1800 m. Large cornices are present throughout the region and are capable of triggering large avalanches when they fail. Cornice failures are most common during windy or warm weather.
About a metre of snow covers a weak layer of facets buried mid-February. Slightly deeper there is a widespread persistent weak layer from late January/early February that consists of surface hoar. It is most prevalent around treeline elevations, but likely reaches into the alpine and in openings below treeline too. These layers are both significantly shallower in the east of the region. Steep, rocky slopes with a shallow or thin to thick snowpack in the alpine and steep, open slopes at treeline are the most likely places to trigger these persistent weak layers. Large loads such a cornice falls or multiple sleds on the same slope often trigger slopes that single rider couldn't trigger.
Terrain and Travel
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Avoid lee and cross-loaded terrain.
- Avoid slopes that sound hollow or drum-like.
- Be aware of the potential for large avalanches due to the presence of a deep persistent slab.
Problems
Wind Slabs
Southwesterly winds have formed wind slabs on lee and cross-loaded features below alpine ridgetops.
Large cornices are present throughout the region and are capable of triggering large avalanches when they fail. Cornice failures are most common during windy or warm weather.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood
Expected Size
Persistent Slabs
The persistent slab problem appears to have been put to rest in deep snowpack areas in the west of the region, but on the eastern slopes (e.g. Kakwa/Tumbler Ridge) there were large natural avalanches last week.
Steep, rocky slopes with a shallow or thin to thick snowpack in the alpine are the most likely places to trigger these persistent weak layers.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 19th, 2021 4:00PM
