Substantial snowfall is forecast for the south of the region (e.g., Manning, Coquihalla); hazard ratings are for these areas. Treat the hazard as one step lower in the north (e.g., Duffey, Hurley).
A couple problematic layers exist around 40 to 80 cm deep, including weak layers of surface hoar and faceted grains above a hard melt-freeze crust. There has not been notable avalanche activity on these layers but Monday's storm could be the tipping point in the south of the region.
Monday's storm is forecast to bring anywhere from 20 to 40 cm of snow to the south of the region. Expect avalanche activity during periods of rapid loading. The safe bet will be to avoid exposure to avalanche terrain once you notice 2+ cm of snow accumulate per hour.
For the entirety of the region, wind slab avalanches are likely to be found adjacent to ridges due to recent strong southwest wind.
SUNDAY NIGHT: Partly cloudy, 20 to 40 km/h west wind, alpine temperature -7 C.
MONDAY: Snow, accumulation 20 to 40 cm in the south of the region and 5 cm in the north, 30 to 40 km/h southwest wind in the south and 20 to 30 km/h north wind in the north, alpine temperature -7 C.
TUESDAY: Clear skies, 10 to 20 km/h north wind, alpine temperature -10 C.
WEDNESDAY: Mix of sun and cloud, 10 km/h southwest wind, alpine temperature -2 C.
Large wind slab avalanches were triggered naturally on Sunday at treeline and alpine elevations from southwest to north aspects.
Avalanche activity is expected to spike in the south of the region during Monday's storm. In the north, wind slabs and perhaps persistent slabs could still be triggered by riders.
Wind slabs are likely to be found at treeline and alpine elevations on northerly to easterly leeward slopes. In the south of the region, new slabs may form rapidly over the day as 20 to 40 cm of snow is forecast to accumulate.
Two concerning weak layers are present in the snowpack. The shallower layer, being around 30 to 70 cm deep, includes feathery surface hoar crystals. There is uncertainty in the distribution of this layer, but the most likely place to find it would be in terrain features sheltered from the wind around treeline and lower alpine elevations. The more widespread layer in the snowpack is a melt-freeze crust from early December, which may have a weak layer of sugary faceted grains above it. This layer is generally found around 40 to 80 cm deep and has produced varying test results in the region. This layer should be treated as suspect were you find faceted grains above the crust.
The remainder of the snowpack is well-settled in the south of the region. In the north, another melt-freeze crust with associated faceted grains around it lies near the ground. The most recent avalanche activity observed on this layer was on December 1st when a cornice fall triggered a size 3 avalanche. More recent snowpack tests in the Cayoosh zone found this layer down 100+ cm and unreactive. While our uncertainty around the reactivity of this crust is keeping it on the radar, it does not appear to be an active problem at this time.
