Continue to make conservative terrain choices while the storm snow settles and stabilizes. Reactive slabs are still a concern for riders below ridgelines and around steep open slopes.
The early December crust can be found down 90 to 150 cm below the surface. While activity on this interface has really tapered off, the recent storm snow has increased the load on this layer and potentially its reactivity. If triggered, this layer has the potential to be larger than expected, thus being very destructive.
Recent low-density snowfalls (30-40 cm) along with constant 50 km/h southerly wind are continuing to develop reactive storm slabs at all elevations. These snow instabilities include loose dry avalanches in sheltered areas and wind slabs in lee terrain near mountain tops. If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
The intense winter storm will ease off Friday night. A weak ridge of high pressure will strengthen over the Interior and generate strong outflow winds along with residual flurries for the weekend. A warm front is expected to invade the region Monday night, with widespread snow and significantly warmer temperatures.
FRIDAY NIGHT: Snow 5 cm / Freezing level at valley bottom / Moderate west wind / Low of -15
SATURDAY: Flurries / 5-10 cm overnight / Freezing level at valley bottom / Moderate west wind peaking up to 60 km/h at night / High of -12
SUNDAY: Cloudy / Freezing level around 500 m/ Moderate to strong southwest wind / High of -10
MONDAY: Snow / Freezing level around 500 m / Moderate south wind / High of -5
Widespread loose dry avalanches were observed on unsupported features at treeline and below during the storm. Storm snow was very reactive to riders, as they were able to easily trigger soft slabs avalanches up to size 1.5 within the new snow.
The limited visibility in the alpine restricted observations on Thursday and Friday, but we suspect that a natural avalanche cycle occurred at night Thursday or early morning Friday.
Although this layer has seen more activity in the south and east region (details and photos here) it remains a serious concern for the South Columbias region, particularly as the current storm is rolling in.
The region received 30 to 40 cm low-density snow and consistent 50 km/h southerly wind since the start of the storm Thursday. This new snow is falling on a variety of surfaces, thin sun crust on solar aspects, isolated surface hoar at treeline on sheltered slopes, fresh wind slabs in lee alpine features at treeline and above or even previous storm snow (20-50 cm) from the last weekend's storm.
We're actively monitoring the early December crust. In some places, it's scoured and on the surface, while in wind-loaded terrain features it can be found as deep as 150 cm below the surface. It consists of faceted grains above a bulletproof crust formed by the Atmospheric Rivers of early December. Avalanches failing on this interface have the potential to be very large.
