Avalanche Forecast
Issued: Jan 1st, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
ahanna,
Avalanche Canada
Conservative terrain selection is critical right now. A buried weak layer has produced a number of large and surprising natural and skier triggered avalanches this week. Find out more in the avalanche summary under the details tab.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Saturday night: Cloudy. Moderate southwest wind. Treeline temperature around -18 C.
Sunday: Flurries starting in the afternoon, 5-10 cm. Moderate to strong southwest wind. Treeline high of -11 C.
Monday: 15-30 cm new snow. Strong southwest wind. High of -7 C.
Monday: 5-10 cm new snow. Light southwest wind. High of -8 C.
Avalanche Summary
There has been an alarming pattern of large, persistent slab avalanches being reported each day this week.
On Friday, a skier triggered a size 3.5 (very large) avalanche on Whale's Back near Nelson. The crown was over 500 m wide, the slide wiped out 30 year old timber and the debris piled 6 m deep. The previously tracked slope was triggered from on top of a ridge/rib feature, where the snowpack is likely thinner. This is a good example of smart terrain travel as the skier who triggered it from the rib was not caught in the avalanche.
Also on Friday, another skier triggered avalanche was reported at Apex mountain, just west of the region. This one was a remotely triggered wind slab and the skier was caught but uninjured.
On Thursday, evidence of a natural size 2.5 persistent slab avalanche was observed on a northeast aspect at 2000m in the Bonnington Range.
On Wednesday, a skier triggered size 2 storm slab stepped down to the early December crust at Kootenay Pass and a naturally triggered size 3 persistent slab was reported in this MIN post from near Rossland.
On Tuesday, explosive control work at Kootenay Pass produced numerous persistent slab avalanches failing on the early December crust, up to size 3.5.
On Monday, several riders were involved in a human triggered size 2.5 persistent slab avalanche near Nelson. The avalanche occurred on a southeast aspect at approximately 1900 m. The treeline slope was heavily wind effected and the rider triggered the avalanche from a thin spot where the layer was only around 60 cm deep. Here is the MIN report of the incident.
Snowpack Summary
With plenty of soft, loose snow available for transport, increasing winds are expected to form fresh wind slabs in lee terrain features at upper elevations.
A crust formed in early December has been responsible for numerous very large persistent slab avalanches in recent days. The depth of the crust ranges widely from 50-150 cm and is most likely to be triggered in wind affected terrain near ridgetops.
The lower snowpack is composed of several early-season crusts. It is these basal crusts that are the primary concern for persistent slab avalanches in thin snowpack areas near Rossland.
Nearly all of the recent avalanches have been triggered from shallow spots in the snowpack where the crust is less than 100 cm deep. Avoid steep, rocky slopes with a shallow or thin to thick transitions in the snowpack.
Terrain and Travel
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
- It's critical to stay disciplined and choose only well supported, low consequence lines.
Problems
Persistent Slabs
A persistent slab problem associated with a crust buried 50-150 cm deep has produced a number of large and surprising avalanches recently. This problem is most likely to be triggered from thin or variable depth snowpack depth such as wind affected features, ridge crests, and near rocky outcroppings.
As you make decisions about where to be and how to move through terrain, try to think in terms of consequences of the worst case scenario just in case you get surprised. "If I trigger an avalanche from here, how big could it be? Am I in a spot where I could get caught in it? Will other people get caught in it?"
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Fresh wind slabs are likely to form at upper elevations as winds build in advance of the next storm. If triggered, wind slab avalanches may step down to deeper layers resulting in larger avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 2nd, 2022 4:00PM
