Avalanche Forecast
Issued: Dec 9th, 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
Danger has increased as wind and new snow form fresh wind slabs throughout the day. Seek out wind sheltered terrain where you can avoid these wind slabs and find great riding.
Summary
Confidence
Weather Forecast
Thursday Overnight: Winds increasing strong to extreme from the southwest as the front moves into the northwest ranges. Light to moderate precipitation overnight with 5-10cm of accumulation. Freezing levels at valley bottom with alpine temperatures around -12 C.
Friday: A stormy day. Strong to extreme southwest winds with moderate to heavy precipitation, 15-30cm of accumulation. Freezing levels rising to around 500m, alpine temperatures around -8 C.
Saturday: Cloudy with continued light precipitation. Winds easing to moderate to strong from the southwest at ridgetop. Freezing levels at valley bottom with alpine temperatures around -15 C.
Sunday: Mainly cloudy with scattered flurries, 2-5 cm accumulation. Moderate westerly winds at ridgetop, alpine temperatures around -15 C.
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.
On Thursday, our field team was out in the Telkwa mountains, they saw a few natural cornice failures up to size 2. Keep in mind that cornice failures have the potential to put a large load on the snowpack and trigger deeper layers.
If you do head out in the backcountry, please share your observations to the Mountain Information Network!
Snowpack Summary
Up to 40 cm of new snow has fallen in the past week with another 10-20 cm expected throughout the day today. Strong to extreme southwest winds will redistribute this new snow into new wind slabs in the alpine and treeline. These new wind slabs will overlie older wind slabs from earlier in the week, amongst a variety of hard, wind effected surfaces.
Below 1400m, a thin rain crust exists below the new snow. There have been reports of faceting around this crust with recent cold temperatures. A spotty surface hoar layer has been reported down ~100cm in the alpine and treeline.
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. With the 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 150-200 cm, with higher values in the western part of the region, tapering to the east.
Terrain and Travel
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
- Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
- Seek out sheltered terrain where new snow hasn't been wind-affected.
Problems
Wind Slabs
Southwest winds will redistribute new snow into wind slabs in the alpine and treeline. These wind slabs may overlie a weak layer of facets or a thin rain crust below 1300m. 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 the snow and wind today we are definitely keeping an eye on it, and would be avoiding large features, overhead hazard, and areas with thin to thick snowpack transitions.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 10th, 2021 4:00PM
