Avalanche Forecast

WEDNESDAY NIGHT: Cloudy with flurries bringing 10 cm of snow to the Monashees and 5 cm to the Selkirks, moderate wind from the southwest, treeline temperatures around -8 C.

THURSDAY: Snowfall continues with another with 10-15 cm in the Monashees and 5-15 cm in the Selkirks, strong wind from the southwest, treeline temperatures warming to -4 C with freezing level reaching 1000 m.

FRIDAY: Mix of sun and cloud, light to moderate wind from the northwest, treeline temperatures around -2 C.

SATURDAY: Mostly sunny, light wind from the northwest, warming temperatures with a possible inversion developing above freezing temperatures between 1500 and 2200 m.

We are coming out of a period of notable avalanche activity. On Monday and Tuesday we saw numerous very large (size 2.5-3) deep persistent slab avalanches occurring in both the Selkirks and Monashees, although the most widespread activity was along the Highway 1 corridor in the Selkirks. These avalanches failed on the early December facet/crust layer which was typically 100-150 cm deep. One notable pattern is that many of these avalanches released at relatively low elevations (1700 to 2000 m) in open clearings, burns, and slide paths. In many cases, they were triggered by smaller avalanches that started at higher elevations.

In addition to the cycle of very large avalanches, there were also numerous reports of smaller storm and wind slab avalanches reactive to human triggering (for example, this MIN report near Revelstoke).

On Thursday, we will likely see reactive slabs form with the new snow and the looming possibility that smaller avalanches could step down to produce very large avalanches in some atypical types of terrain.

Expect 10-25 cm of new snow on Thursday, with the heaviest accumulations around Revesltoke and in the Monashees. This incoming snow is burying recently formed sun crust and suface hoar layers, which means we could see thin and reactive slabs. Some complex layers have formed in the top 50 cm of the snowpack over the past week, including several crusts and surface hoar layers in isolated areas. In southern parts of the region, crust layers are much closer to the surface. While none of these upper layers are necessarily going to remain a long-lasting problem, there is a fair bit of uncertainty about their spatial distribution and whether they will be reactive in the upcoming week.

The primary weak layer that remains a widespread concern across the Columbias is a deeply buried crust/facet layer that formed in early December. It is typically down 100-150 cm, but as deep as 200 cm in wind loaded terrain. There has been regular avalanche activity on this layer at all elevations for over a month, and we expect to see avalanche activity continue on this layer.

• It's critical to stay disciplined and choose only well supported, low consequence lines.
• Use increased caution at all elevations. Storm snow is forming touchy slabs.
• Dial back your terrain choices if you are seeing more than 20 cm of new snow.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.
• Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.