Conditions are more complicated than what meets the eye. Fresh wind slabs formed 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.
Westerly wind redistributed 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 than expected avalanche.
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.
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!
Up to 20 cm new low-density snow was redistributed by westerly wind that formed fresh wind slabs in the alpine and at treeline. In sheltered terrain, cold temperatures likely maintained 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 whumpfing, 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.
Tuesday night
Mostly cloudy with a trace of new snow. Westerly wind 30 km/h at ridgetop. Treeline temperature low -11 °C.
Wednesday
Mostly cloudy with a trace of new snow. Westerly wind 20-30 km/h at ridgetop. Treeline temperatures reach a daytime high of -8 °C.
ThursdaySunny periods but mostly cloudy with snowfall, up to 10 cm of accumulation is possible. Southwesterly wind 30-50 km/h at ridgetop. Treeline temperatures reach a daytime high of -6 C.
FridayMostly cloudy with isolated flurries, up to 5 cm of accumulation is possible. Southwest wind 20 km/h at ridgetop. Treeline temperature high -6 °C.
More details can be found in the Mountain Weather Forecast.
