Avalanche Forecast
Issued: Dec 6th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Deep Persistent Slabs.
bchristie,
Avalanche Canada
Choose wind sheltered terrain, and avoid features steeper than 25 degrees where the new snow is falling on a hard crust.
Be wary of thin, rocky start zones. There is potential for a rider to trigger deep avalanches.
Summary
Confidence
Weather Forecast
Monday Night: Mostly cloudy. No new snow expected. Moderate southwest wind. Alpine temperature above -10, with a possible temperature inversion.
Tuesday: Overcast. 20-30 cm snow expected. Strong to extreme southwest winds. Freezing level rising to 250 m, potentially up to 1000 m in the south of the region. Alpine temperature around -5. Temperature inversion breaking down.
Wednesday: Mostly cloudy. 5-20 cm snow expected. Moderate to strong west winds. Freezing level dropping back to valley bottom, with alpine temperatures around -10 C.
Thursday: Partly cloudy. 0-5cm snow expected. Moderate southwest winds. Alpine temperature around -8.
Avalanche Summary
On Sunday, near Ningunsaw, and in the Nass River valley, large avalanches were reported to have failed near the ground. This adds to the report late last week from Bear Pass of some very large, explosive triggered avalanches, keeping thoughts of a deep persistent weak layer in our minds.
Late last week, natural, explosive, and cornice triggered slab avalanches were reported up to size 3.
Expect natural and rider triggered avalanches to occur as we receive significant new snow and wind.
Snowpack Summary
There are recent reports of large to very large avalanches running on or near the ground in Bear Pass, Ningunsaw, the Nass River Valley, and around Smithers. We don't know how widespread this problem may be, or if all events reflect the same avalanche problem, but we are definitely keeping an eye on it, and would be avoiding large features and areas with thin to thick snowpack transitions for now.
Due to recent, variable winds, you may find wind slabs on many aspects, and on both sides of ridges. Some exposed areas may be stripped back to the Nov 30/Dec 1 Crust. This crust exists up to 2000 m in the southwest of the region, and may only be found up to 1200 m in areas east of Terrace.
There are reports from around the region of surface hoar forming at and below treeline. This could be a touchy new sliding layer when it gets buried on Tuesday, especially where it will be sitting on a crust.
Treeline snowpack depths are estimated to be around 2-3 m, and a prominent crust can be found near the base of the snowpack.
Terrain and Travel
- Storm slab size and sensitivity to triggering will likely increase through the day.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Problems
Storm Slabs
The recent forecaster blog does a great job of capturing the challenging travel and decision-making we'll likely encounter in the backcountry right now.
Slabs may be especially reactive where they sit on top of a crust.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Deep Persistent Slabs
Avoid large features, and thin rocky start zones. We are still uncertain about the distribution of this weak layer. Recent reports of avalanches that failed on this layer are in the northern half of the region.
Aspects: All aspects.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Dec 7th, 2021 4:00PM
