Avalanche Forecast
Regions: Bonnington, Grohman, Kootenay Boundary, Kootenay Pass, Moyie, Norns, Rossland, St. Mary, Ymir.
Conditions are more complicated than what meets the eye. Fresh wind slabs are expected to form at upper elevations. Riders may be drawn to more sheltered areas around treeline to avoid these wind slabs, but should consider that this is where the persistent slab problem has been most problematic to date. Keep your terrain choices conservative and don't let good riding lure you into steeper terrain.
Confidence
Moderate
Avalanche Summary
A layer of surface hoar from mid-November buried 40-80 cm deep continues to be reactive. Widespread whumpfing and cracking continue to be reported, with the most reactivity observed in sheltered and shaded areas at treeline.
On Friday, a remotely triggered natural avalanche was reported on a steep east-facing feature near Kootenay Pass, likely failing on this layer. Read the MIN report here.
Thank you for all the great MIN reports! They are extremely helpful to us in the early season when snowpack information is limited. Keep them coming!
Snowpack Summary
Overnight and throughout the day 5-10 cm of new snow is expected. In wind-affected terrain, westerly winds are expected to redistribute this new snow into fresh wind slabs. In sheltered terrain, cold temperatures will likely maintain low-density, powdery snow.
On south-facing aspects, a crust may be found below the new snow from solar radiation and warm temperatures on Sunday.
There are two prominent weak layers in the upper snowpack. A weak layer of surface hoar can be found 30-60 cm down. Another weak interface that was formed during the dry period in mid-November is buried 60-90 cm deep. This layer consists of sugary faceted grains, large surface hoar crystals in sheltered terrain features, and a crust on steep sun-exposed slopes. Reports of whumping, cracking, and recent avalanches suggest these interfaces are not bonding well.
We have limited information at this point in the season, we're hoping to gain more information on the distribution and sensitivity of these layers as we collect more field observations.
Snowpack depths average 80-160 cm in the alpine. Below treeline elevations are now above the threshold for avalanches in many areas.
WednesdayWeather Summary
Monday night
Cloudy with light snowfall, up to 5 cm of accumulation expected. Westerly winds increasing 25-40 km/h at ridgetop. Treeline temperatures drop to -11 C.
Tuesday
Cloudy with continued snowfall, up to 5 cm of accumulation expected. Westerly winds 25-40 km/h at ridgetop. An alpine temperature inversion may be present, with alpine temperatures around -10 C and valley bottom temperatures close to -15 C.
WednesdayCloudy with light snowfall, up to 5 cm of accumulation. Westerly winds 20-30 km/h at ridgetop. Treeline temperatures reach a daytime high of -5 C.
ThursdayCloudy with snowfall, up to 10 cm of accumulation is possible. Southwesterly winds 30-50 km/h at ridgetop. Treeline temperatures reach a daytime high of -6 C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
- Remote triggering is a concern, watch out for adjacent and overhead slopes.
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
Avalanche Problems
Persistent Slabs
Two surface hoar layers in the upper snowpack are showing reactivity to natural and human triggers.
The primary concern is a large surface hoar layer buried mid November around 40-80 cm deep, above weak facets and a widespread melt freeze crust.
This problem is thought to be most tricky at treeline elevations. Terrain features here may be sheltered enough to preserve surface hoar but also hold a cohesive slab of wind affected snow above, creating primed conditions for human triggering.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 2.5
Wind Slabs
Westerly winds are expected to redistribute the loose, powdery surface snow into fresh and reactive wind slabs in the alpine and open areas at treeline.
It is possible small avalanches in the upper snowpack could trigger deeper weak layers, creating a larger then expected avalanche.
Aspects: North, North East, East, South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2