A weak layer of surface hoar continues to be a concern, particularly around treeline. Uncertainty surrounding this layer is best managed by conservative terrain choices and a cautious approach to risk management.
Watch for signs of instability like recent avalanches, whumpfing, or shooting cracks.
Watch for reactive wind deposited snow on all aspects, recent winds have varied from southerly to northwest.
There's a lot of loose snow out there, expect fresh slabs to form if the wind picks up.
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 60-80 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 60-80 cm deep continues to be reactive. Widespread whumpfing and cracking continue to be reported.
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. On Thursday, evidence of a natural cycle was observed to size 2 on north-facing terrain features around 2000 m.
Several other MIN reports from across the forecast region indicate the sensitivity of these layers, showcasing whupping, cracking, and reactive snowpack tests (MIN).
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!
Cold temperatures and clear skies over the past few nights will promote surface hoar growth and faceting on the surface of the snowpack.
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.
TuesdaySunday night
Mainly clear, increasing high cloud in the morning. Westerly wind 10-25 km/h at ridgetop. Treeline temperature drops to a low of -18 C.
Monday
Mainly cloudy, light snowfall with trace accumulation. Westerly wind 10-35 km/h at ridgetop. Treeline temperature high of -9 C.
TuesdayCloudy with snowfall, up to 5 cm of accumulation expected. Westerly winds 15-40 km/h at ridgetop. Treeline temperatures reach a high of -10 C.
WednesdayA mix of sun and cloud, light snowfall possible with trace accumulation. Westerly winds 10-30 km/h at ridgetop. Treeline temperatures reach a high of -9 C.
More details can be found in the Mountain Weather Forecast.
