Avalanche Forecast
Issued: Dec 7th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Deep Persistent Slabs.
zryan,
Avalanche Canada
Investigate the bond of new wind slabs to the old surface. In many areas, wind slabs will be sitting on top of a weak layer of facets or surface hoar, making them more reactive to rider triggering.
Summary
Confidence
Weather Forecast
Tuesday Overnight: 2-10cm of new snow accompanied by strong to extreme southwest winds. Freezing levels at valley bottom with alpine temperatures around -10 C.
Wednesday: A mainly cloudy day with 2-5 cm of new snow, heaviest in the morning. Winds shifting west and easing in the moderate to strong ranges. Alpine temperatures dropping to around -15 C.
Thursday: A quieter day with a brief ridge of high pressure developing in northern BC. Partially cloudy with flurries. Accumulation up to 3cm. Moderate to strong NW winds.
Friday: A strong frontal system will move over the region, bringing strong to extreme SW winds, freezing levels rising to 1000m, and up to 15cm of new snow. Heaviest in the afternoon and increasing into the evening.
Avalanche Summary
On Saturday, a size 3 avalanche was reported in the Hankin-Evelyn area, failing near the ground. This has us thinking about the potential for a deep persistent weak layer.
If you do head out in the backcountry, please share your observations to the Mountain Information Network!
Snowpack Summary
2-10 cm of new snow overnight will be redistributed into wind slabs in the alpine and treeline by strong to extreme southwest winds. Prior to the new snow, cold and clear nights have promoted faceting and surface hoar growth on the snow surface. This will create a touchy sliding layer for new wind slabs, especially where it overlies a crust.
Exposed areas may be stripped back to the Dec 1 Crust. This crust has been reported up to 1600m in the south end of the region.
An early season crust can be found near the base of the snowpack. It has shown reactivity in the past week with large loads (explosives' and cornice), creating large avalanches. We don't know how widespread this problem may be, but with incoming snow and wind we are definitely keeping an eye on it, and would be avoiding large features and areas with thin to thick snowpack transitions.
Snowpack depth at treeline ranges from 100-250 cm, alpine depths average 200-300 cm.
Terrain and Travel
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
Problems
Wind Slabs
New snow and wind will create wind slabs in the alpine and treeline. These wind slabs will overlie a weak layer of facets and in some areas surface hoar. These weak layers will increase both the reactivity and propagation potential of wind slabs, particularly when a crust is present below.
Aspects: North, North East, East, South East, South, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
An early season crust near the base of the snowpack has shown reactivity in the past week with large explosives' and cornices. With incoming snow and wind we are definitely keeping an eye on it, and would be avoiding large features and areas with thin to thick snowpack transitions.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 8th, 2021 4:00PM
