With forecast snow, rain and strong wind the avalanche hazard is on the rise for Tuesday. Reactive slabs may exist at higher elevations and loose wet avalanches below. The new load and stress on the snowpack may be enough to trigger deep weak layers.
Weak surface hoar and/or faceted grains sit above a melt-freeze crust around 70 to 100 cm deep. The likelihood of triggering a persistent slab has reduced, but the consequence of doing so remains high.
New storm slabs will continue to build Tuesday. The new snow/ rain load will destabilize the snowpack and natural avalanches are likely. New wind slabs are expected to form at higher elevations due to strong southerly wind.
Rain will soak the snowpack below the snow-rain line (forecast below 1800 m). Natural and human triggered wet snow avalanches are likely on Tuesday.
A strong Pacific frontal system will push inland Tuesday bringing heavy precipitation, rising freezing levels, and strong wind.
Overnight Monday: Snow 10-20 cm with the higher amounts South (KPass). Ridgetop wind moderate from the southwest. Freezing levels near 1100 m.
Tuesday: Snow 20-35 cm throughout the day (again expect the higher amounts for KPass) with strong ridgetop wind from the southwest. Freezing levels rising to 2000 m later in the day.
Wednesday: Snow 10-20 cm. Ridgetop wind strong to extreme and freezing levels near 1800 m.
Thursday: Mix of sun and cloud with temperatures falling to -6 degrees and freezing levels near 1000 m. Ridgetop wind mostly light with strong gusts expected.
No new avalanche reports on Monday. With new snow/rain and rising freezing levels on Tuesday, the avalanche hazard will be on the rise. Natural and human triggered avalanches are likely.
Of note, a naturally-triggered size 3 deep persistent slab avalanche released on a southeast aspect at 2200 m in the Rossland range last Tuesday or Wednesday. The avalanche likely failed on the weak layers described in the Snowpack Summary and scrubbed to ground. Persistent slab avalanche activity has quieted in the past few days since this report. Although the likelihood of triggering these layers has reduced, the consequence of doing so remains high.
New and reactive storm and wind slabs will continue to build Tuesday. The storm is expected to drop around 10 cm Monday night and another 20-30 cm Tuesday. The storm will come with strong southwest wind so wind slabs are expected at higher elevations. Treeline and below treeline elevations may see a loose wet avalanche cycle where the precipitation falls as rain. In sheltered areas, this snow may overlie surface hoar.
Two weak layers are buried in close proximity to one another. They are 70 to 100 cm deep around Nelson and 50 to 80 cm deep around Rossland and other western parts of the region. The layers are composed of surface hoar and faceted grains and they overlie a hard melt-freeze crust. Many MIN reports describe these layers and their snowpack test results. The results suggest that it remains possible for riders to trigger these layers.
Another layer of faceted grains above a melt-freeze crust that formed in early November is upwards of 200 cm below the surface. This has been the suspected failure layer of a few very large avalanches that released last week in the Rossland range.
