Regions
Kootenay Boundary.
New snow and wind Sunday night and Monday are expected to produce a natural avalanche cycle. Forecast warming Tuesday won't help matters. Only very cautious and conservative terrain choices are appropriate at this time.
Confidence
Low - Due to the number of field observations
Weather Forecast
A series of Pacific storms will continue to impact the Kootenay Boundary with the general theme being periods of heavy precipitation and strong winds interspersed with showery blustery conditions. A significant rise in freezing levels is possible with Tuesdays storm as mild sub-tropical air is drawn into the frey. SUNDAY NIGHT: Freezing Level 1500m, 2 to 15cm of snow, strong SW winds. MONDAY: Freezing level around 1500m, 4 to 25cm of snow, strong SW winds. TUESDAY: Freezing level forecast to rise to 2500m. 5 to 15mm of precipitation falling as rain below 2500m. Strong SW winds. WEDNESDAY: Freezing level lowering from 2500m to 1700m. 1 to 8cm of snow possible with strong SW winds.
Avalanche Summary
On Saturday natural storm slab avalanches to size 2 were reported on East, North, and Northwest facing features between 1900 and 2100m. These were likely running on the early December surface hoar. Late Sunday we received a report from the Rossland range where a group of skiers triggered a size 2.5 avalanche on a north facing piece of terrain at 1700m. The avalanche initially failed at the Mid-November crust before stepping down to the ground. Thankfully, it sounds like everyone involved will be okay.
Snowpack Summary
Snow depth in the region is between 100 and 160cm. In the last few days the successive storms have laid down 30 to 60cm of storm snow. This storm snow rests on a variety of old surface including loose faceted snow, the well advertised early-December surface hoar in sheltered locations at and below treeline, and a crust at upper elevations (especially on southerly aspects). The mid-November crust is just under the new storm snow and quite robust. It's been reported as being 1 to 8cm in thickness. A human triggered avalanche Sunday ran on this crust and we suspect it's just starting to wake up. The next few days should tell us a lot about this interface.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.