Conditions remain complicated in the alpine from shifting winds, a skiff of new snow, and weak layers below. Be prepared to assess conditions, avoid overhead hazard, and adjust your travel as you gain elevation.
Winds have drifted the recent storm snow into slabs on leeward features that may remain prone to human triggering. Winds have shifted from extreme out of the southwest to moderate out of the northwest, creating a tricky loading pattern in the alpine and potentially bringing cornices to their breaking point.
A layer of weak, sugary facets persists at the bottom of the snowpack. Triggering deep persistent slab avalanches is more likely in snowpack areas that transition from thick to thin, like in shallow, rocky start zones. Easier-to-trigger wind slab avalanches or cornice falls could step down to this deeper layer, resulting in very large avalanches.
Sunday night: Partly cloudy, isolated flurries with trace accumulations, light northwest winds, alpine temperature -13 C.
Monday: Partly cloudy, isolated flurries with trace accumulations, light northwest winds, alpine high temperature -10 C.
Tuesday: Increasing cloud, light southwest wind, alpine high temperature -10 C.
Wednesday: Cloudy, isolated flurries with trace accumulations, light southwest winds gusting at ridge-top, alpine high temperature -8 C.
During the storm, numerous size 2-3.5 slab avalanches were observed releasing naturally in the storm snow. A few were thought to have stepped down to deeper layers. These avalanches primarily occurred on leeward aspects, mainly at treeline and alpine elevations. Reports indicate that cornices may be reaching their breaking point and may act as triggers for these avalanches. Below tree line, wet loose avalanches were releasing naturally during the warm temperatures on Saturday.
Over the past week, there have been several deep persistent slab avalanches reported in the region. Two were triggered by explosives and one that occurred near Golden was remotely triggered by humans. This activity outlines the fact that this layer remains a problem in the region. Large alpine features, especially rocky, thin snowpack areas are the most likely places to trigger this layer. Easier-to-trigger wind slab avalanches or cornice fall may have the potential to step-down to this layer.
There have been substantial changes to the snowpack over the past few days. 40-60 cm of snow fell during the weekend storm above 1900 m. Higher snow totals fell in the northern and western parts of the region. Extreme winds originating from the southwest and shifting to the northwest have created a tricky loading pattern in the alpine and have elevated concern for cornice triggers. These winds drifted the snow into deeper, stiffer slabs on leeward terrain features that may remain prone to human triggering. During a warming event Saturday night, rain saturated snow surfaces up to around 1900 m that have since refrozen with cooling temperatures.
A weak layer of surface hoar may still be found about 90 cm deep around Golden and Kimberley, 50 cm deep around Invermere, and 130 cm deep along Kootenay Lake.
As usual for the Purcells, the base of the snowpack contains basal facets and it remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall or explosives.
