A widespread natural avalanche cycle is expected to occur on Wednesday. Travel in avalanche terrain, including areas exposed to overhead hazard, is not recommended.
Several different deeply buried weak layers can be found in the snowpack that have produced large avalanches. Rapid loading from new snow and wind is expected to test these persistent weak layers with a critical load. Shallower, more reactive storm slabs carry the risk of triggering one of these deeper weak layers to create larger, more destructive avalanches.
Ongoing snowfall is covering a new layer of surface hoar observed across the region while burying another recent surface hoar layer even more deeply. New snow is expected to become increasingly easy to trigger as its depth increases. Slab problems will become widespread, with wind-loaded areas seeing more slab formation and with sheltered areas holding more pronounced weak layers.
Tuesday night: Cloudy, 10-20 cm of snow, moderate to strong southwest winds, alpine temperatures near -3 C with freezing levels around 1200 m.
Wednesday: Mostly cloudy, another 5-15 cm of snow, moderate to strong west winds, alpine high temperatures near-2 C with freezing levels around 1300 m.
Thursday: Mix of sun and cloud, isolated flurries with a trace of accumulation, moderate west winds, alpine high temperatures around -5 C with freezing levels dropping below 500 m.
Friday: Cloudy, 10-20 cm of snow, moderate to strong southwest winds, alpine high temperatures near -1 C with freezing levels rising to 1600 m.
Numerous and widespread natural avalanches were reported Tuesday as snow accumulated over a recent layer of surface hoar. These avalanches were small (size 1.5), but expect avalanche size to increase as snowfall continues.
Several persistent slab avalanches (size 1.5-3), both human and explosive-triggered, were reported over the weekend. These avalanches released on both the December surface hoar and November crust layers across a variety aspects. This recent persistent slab avalanche was observed Sunday. It scrubbed into the lower snowpack and to the ground and was noted for being triggered on a shallow, rocky, convex slope.
The possibility for large human-triggered persistent slab avalanches remains a serious concern, especially as newly formed reactive storm slabs create the potential for avalanches to step-down to these layers.
Overnight snowfall is forecast to bring storm snow totals to 35-50 cm for most of the region (with areas like Big White potentially seeing 60+ cm). This will create a widespread storm slab problem at all elevations that will need to be managed conservatively. In the alpine, moderate southwest winds are expected to exacerbate the reactivity of the new snow in drifted areas. The new snow is falling on another recent layer of surface hoar that has been showing increasing reactivity as snow accumulates.
Buried deeper in the snowpack, there are multiple weak layers, which include a feathery surface hoar layer (down 80 to 120 cm), an older surface hoar layer with a melt-freeze crust on steep south aspects (down 100 to 140 cm), and a layer of sugary faceted snow, surface hoar, and melt-freeze crusts from late November found in the bottom half of the snowpack.
Snowpack tests continue to produce sudden and propagating results on these layers (like this MIN from Big White on Sunday and this MIN from Rossland on Monday) This fundamentally unstable snowpack structure remains a serious concern as new snow and wind add an additional load and increase the likelihood of triggering large and destructive avalanches.
