Avalanche Forecast

A storm system is forecast to bring substantial snowfall to the region on Sunday night and Monday with strong winds. 

Sunday night: Snowfall 15-20 cm, moderate to strong SW wind, treeline temperature around -12 °C. 

Monday: Snowfall 15-25 cm, moderate to strong SW wind, treeline high around -8 °C. 

Tuesday: Mainly cloudy with a chance of flurries, light to moderate SW wind, treeline high around -8 °C. 

Wednesday: A mix of sun and cloud, light to moderate NW wind, treeline high around -10 °C. 

On Saturday, new reports were limited to skiers triggering size 1 loose dry avalanches in steep terrain.

On Monday, new storm slabs are expected to form with the incoming storm system and strong winds. These new slabs will sit on a weak snow surface and may be very reactive, especially in wind loaded terrain. The persistent slab problem remains a serious concern and the weight of the new snow may increase the reactivity of these deeper layers. Smaller storm slab avalanches also have the potential to step down to deeper layers resulting in very large avalanches. 

There has been an alarming pattern of large, persistent slab avalanches being reported each day last week. This blog post goes into additional details on the problem.

On Friday, a skier triggered a size 3.5 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 2000 m 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 December 27, 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.

The new storm snow buries a variable snow surface which is likely very weak and includes widespread facets, wind affected surfaces, and/or spotty surface hoar up to 4 mm in sheltered areas. The new snowfall is expected to be accompanied by strong winds and reactive new slabs are expected to be widespread. 

The early December crust/facet layer has been responsible for numerous very large persistent slab avalanches in the past week. The depth of the crust ranges widely from 50-150 cm and has most recently been reactive 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.

• Storm slab size and sensitivity to triggering will likely increase through the day.
• 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.