Avalanche 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.

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.

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.

• 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.