Fresh snow sits on a particularly reactive interface and remains primed for human triggering. Don't let benign weather lure you into avalanche terrain. Storm slabs have the potential to break larger than anticipated.
Strong southwest winds have redistributed the recent snow into stiffer slabs at upper elevations that are likely to be human triggered. Winds are forecast to shift to the northwest overnight, so watch for freshly formed slabs on a variety of aspects. Cornices may be reaching their breaking point.
The 30-45 cm of snow that fell in the past 24 hours needs more time to bond to the underlying crust, especially in sheltered areas near and below treeline where surface hoar is preserved at the interface.
Sunday night: Cloudy, 5-10 cm of snow, strong ridgetop winds shift from southwest to northwest and decrease to moderate, treeline low temperature near -10 C, freezing level drops to 400 m.
Monday: Cloudy with sunny breaks, isolated flurries with trace accumulations, light northwest winds gusting to moderate at ridgetops, treeline high temperatures near -9 C, freezing level rising to 700 m.
Tuesday: Sunny, no precipitation expected, light northwest winds, treeline high temperatures near -10 C, freezing level near 400 m.
Wednesday: Cloudy, scattered flurries with up to 5 cm of snow, moderate west winds, treeline high temperatures near -8 C, freezing level around 200 m.
On Sunday, operators reported numerous small (size 1-1.5) avalanches breaking in the storm snow with widespread propagation. Avalanches in the new snow remain likely to trigger on Monday. Cornices may reach their breaking point and may act as triggers on slopes below.
Last week, explosive control work near Whistler produced a cornice fall that triggered a size 2.5 deep persistent slab on the weak facetted crystals above the early December crust. The slab broke 60-130cm deep. This indicates that while the weak layer is unlikely to be affected by skiers and riders, it is still triggerable by very large loads.
On Sunday, the mountains picked up 25-45 cm of new snow, with another 5-10 cm forecast to accumulate by Monday morning. The new snow has formed a widespread reactive storm slab problem that is particularly concerning where it sits over a layer of surface hoar near and below treeline. Continue to be disciplined with terrain selection, and closely monitor the bond of the new snow to previous snow surfaces. Be aware of the potential for loose avalanches in terrain where snow hasn't formed a slab.
Winds have been strong to extreme from the southwest, redistributing the new snow into stiffer wind slabs at upper elevations. Winds are forecast to shift to northwest overnight and ease to moderate. Anticipate changing slab conditions as you move into wind-exposed terrain on a variety of aspects.
Below the storm snow, a thick melt freeze crust can be found on all aspects up to approximately 2200 m. Deeper in the snowpack, it is possible to find a crust/facet layer from December that is buried down 100-200 cm. This layer is most prominent between 1700-2100 m and is currently classified as dormant; although large loads such as a cornice failure or avalanches in motion may still be able to trigger avalanches on this layer.
