North Rockies

Strong winds will be the obvious factor driving avalanche danger for the coming days as storm snow is redistributed into new wind slabs, but they aren't the only factor. Our low probability/high consequence persistent slab still needs to figure into your terrain decisions.

MONDAY NIGHT: Partly cloudy with isolated flurries and a trace of new snow. Moderate southwest winds.

TUESDAY: Increasing cloud with scattered flurries bringing up to 5 cm of new snow by end of day, continuing overnight. Moderate to strong south winds, increasing over the day and becoming extreme overnight. Alpine high temperatures around -5 with freezing levels climbing to 1500 metres in the evening.

WEDNESDAY: Cloudy with continuing flurries bringing about 5 cm of new snow, closer to 10 cm with overnight accumulations. Flurries easing over the day. Strong southwest winds. Alpine high temperatures around -6, cooling over the day with freezing levels falling from 1500 to 1000 metres.

THURSDAY: A mix of sun and cloud. Moderate to strong southwest winds. Alpine high temperatures around -5.

Check out this MIN report from the North Rockies field team on Sunday gives an indication of natural avalanche activity that resulted from the weekend storm in the Renshaw area.

A widespread natural avalanche cycle occurred in the region on Friday and produced many avalanches to size 2 (large). The extent to which this cycle involved the persistent weak layers lingering in the region is uncertain, but it seems our persistent slab avalanche problem has fully transitioned into a low-probability/high-consequence situation. 

There were many notable avalanches on persistent weak layers between Dec 18-20 including natural, accidental, and remotely triggered avalanches up to size 2.5 at Pine Pass, Torpy, and Tumbler Ridge. Recent observations like this one from the Tumbler Ridge area show that where these layers are well preserved, they can still fracture energetically with a large trigger.

The region picked up to 55 cm from the weekend storm, with the deeper amounts being found to the north. 40 to 120 cm of snow is now sitting above a mix of weak interfaces that were buried in early December. In some (but not all) terrain these interfaces may be composed of weak surface hoar or weak crusts and facet layers, creating a persistent slab avalanche problem. 

We do not see a clear pattern in which parts of the region or which types of terrain this problem is still a concern. 

Between Dec 18-20 there was compelling evidence of this problem around Pine Pass, the McGregors, and Tumbler Ridge. This problem has not been found at Renshaw, but has been found in the surrounding areas near McBride. There is no recent information from Kakwa. 

Overall, uncertainty about these layers make it difficult to have confidence in challenging or complex avalanche terrain without very careful terrain evaluation and an in-depth understanding of local snowpack conditions.

Snow depths are in 150-250 cm around Pine Pass, the McGregors, and McBride and closer to 100-150 cm around Tumbler Ridge. In shallower areas along the eastern slopes there could be weak snow at the bottom of the snowpack that could be a concern in steep rocky alpine terrain.

• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
• In times of uncertainty conservative terrain choices are our best defense.