Avalanche Forecast
Issued: Jan 9th, 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.
ahanna,
Avalanche Canada
The slope testers have been out in full force and we've seen a sharp drop in natural and human triggered avalanche activity since the end of the week. Even so, watch out for lingering wind slabs and keep in mind the potential for large and destructive persistent slab avalanches.
Summary
Confidence
Weather Forecast
Saturday night: Increasing cloud, isolated flurries, light to moderate southeast wind, freezing level valley bottom.
Sunday: Mostly cloudy, moderate southwest wind, alpine high -7, freezing level 600 m.
Monday: Flurries, up to 5 cm, moderate southwest wind, alpine high -6, freezing level 1000 m.
Tuesday: Snow 5-10 cm, strong southwest wind, alpine high -5, freezing level 1200 m.
Avalanche Summary
Avalanche activity during the week was generally large (averaging size 2), a combination of wind and persistent slabs, triggered both naturally and by humans.
- Wind slab - Numerous natural storm/wind slab avalanches were observed on all aspects at alpine and treeline elevations as recently as Friday, averaging size 2.
- Cornice - A few reports of cornice falls size 1-2 have triggered wind slabs on the slopes below.
- Human triggered - Thursday and Friday were eventful days for human triggered avalanches in the busiest areas of the region. RMR slackcountry saw four size 1.5-2 skier triggered avalanches, including a partial burial. Check out some of these MIN reports here, here and here. Crowns ranged from 30 to 70 cm, likely running on the most recent storm interface at the shallow end, and on the Christmas persistent layer at the deeper end.
- Persistent slab - On Wednesday and Thursday, there were four natural persistent slab avalanches size 2.5-3 reported in the region on northerly aspects in the alpine. Three of these were reported to have run on the early December persistent weak layer.
Snowpack Summary
Around 40-80 cm of recent snow sits on a weak layer of surface hoar that was buried around Christmas. This layer is most prevalent at and below treeline. Previous moderate to strong winds have redistributed surface snow, creating wind slabs at wind exposed elevations.
A couple of persistent weak layers buried in early/mid-December are down about 90-150 cm. Generally, they can be found as a layer of surface hoar above in close proximity to a crust/surface hoar layer. The form and distribution of these layers are highly variable and conditions may differ significantly from one valley to the next.
Terrain and Travel
- Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
- Avalanche hazard may have improved, but be mindful that deep instabilities are still present.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Problems
Wind Slabs
Previous snow and wind have created deep pockets of wind slab in lee terrain features at upper elevations. These were very reactive before the weekend and may remain sensitive to human triggers.
Cornices have also been growing. A cornice fall is a large load that can trigger avalanches on the slope below.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A weak layer of surface hoar that was buried around Christmas is now down about 40-80 cm and is most prevalent at treeline and below. This layer remains at a depth triggerable by skiers, sleds and wind slab avalanches.
A deeper persistent weak layer buried in early/mid-December is now down 90 to 150 cm. Triggering these layers require large loads such as explosives or other avalanches in motion. The result of a step down to these layer would be large and destructive.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 10th, 2021 4:00PM
