Regions
Kootenay Boundary.
With warming temperatures, avalanches may run naturally, especially on steep sun affected slopes. Cornices have grown large and will weaken with rising temperatures. Be conservative with terrain choices.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Tuesday
Weather Forecast
The high pressure ridge over the interior of the province should remain until late Sunday afternoon. Warm southerly winds will continue driving the freezing level to 2500 m late Saturday through Sunday, then begin to drop late on Sunday afternoon to around 1500 m. No overnight temperature recovery expected. Precipitation is forecast to begin late Sunday afternoon and continue through Tuesday with 10 to 15 mm forecast, most likely falling as rain below 1500 m. Wednesday should be dryer with the freezing level dropping to 1000 m overnight.
Avalanche Summary
Reports of natural and human triggered avalanches have dropped off in the past few days. Earlier in the week a skier remotely triggered a cornice failure from a few meters away on a north/northeast facing slope around 2100 m in the Rossland range. When the falling chunks of cornice impacted the slope below it triggered a very large (size 3) avalanche that ran on the March 6th crust. Natural cornice failures have also been reported. A second skier triggered avalanche (size 2) was reported on a northeast facing feature near 2000 m. Numerous loose wet avalanches to size 1.5 have also been reported on solar aspects. ( facing southerly) .
Snowpack Summary
The recent storm snow of 40 to 60 cm continues to settle above multiple crusts at treeline and below. In some valleys these storm slabs may be sitting on a thin crust that was buried on March 11th. A second crust, (the early March melt/freeze crust) can be found down 50 to 80 cm. The late February (Feb 27th) persistent weak layer of buried surface hoar down is now down 70 to 120 cm and has been the interface for some large avalanches. We suspect that this weak layer is more prominent on northerly (shaded) aspects at and above 1700 m. This surface hoar layer may also be associated with a crust on solar aspects. With the forecast of sun and strong solar radiation, triggering this deep weak layer may become easier. Pay attention to moist or wet surface snow as a sign that solar radiation is strong, and the potential is there for deep weak layers to become reactive.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.