Avalanche Forecast
Regions: Bonnington, Grohman, Kootenay Boundary, Kootenay Pass, Moyie, Norns, Rossland, St. Mary, Ymir.
A reactive layer of surface hoar continues to be a concern. Choose conservative terrain and consider that hazard may be most tricky at treeline elevations.
Watch for signs of instability like recent avalanches, whumpfing or shooting cracks.
Confidence
Moderate
Avalanche Summary
A layer of surface hoar from mid November buried 60-80 cm deep continues to be reactive. Widespread whumpfing and cracking were reported on Wednesday and Thursday. 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 touchy cut banks (MIN1), whumpfing and shooting cracks (MIN2), and reactive snowpack tests (MIN3).
Snowpack Summary
Upwards of 40 cm accumulated around the region over the last few days. This covers a layer of small surface hoar now buried 30-50 cm. Another weak interface is buried 60-90 cm deep from mid November - consisting 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 this interface is 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 deeper layers as we collect more field observations.
Snowpack depths exceed 160 cm at upper elevations and below treeline elevations are now above threshold in many areas.
Weather Summary
Saturday Night
Mostly clear skies with light westerly winds. No snowfall expected.
Sunday
Mostly clear skies with light and variable winds. Alpine high of -10. Isolated flurries possible late afternoon.
MondayA mix of sun and cloud, increasing westerly winds over the day to strong or extreme northwesterlies. Alpine high of -9. Flurries bring trace amounts of snow.
TuesdayMostly cloudy with strong to extreme northwest winds around ridgelines. Alpine high of -12. Flurries bring trace amounts of snow.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
- Remote triggering is a concern, watch out for adjacent and overhead slopes.
- Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
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 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.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible - Likely
Expected Size: 1.5 - 2.5
Wind Slabs
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 when the wind picks up.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 2