It's the time of year when avalanche conditions vary widely by elevation. Increase caution as you reach your target of upper elevations where melt freeze crust is thinner or absent. This is also where recent storm snow may still react to human triggers.
Storm slab avalanche activity has been persisting over the last several days, both as a result of sustained stormy weather but also due to a weak storm interface composed of facets and surface hoar in some areas. Remote (from a distance) triggering on Monday speaks to touchy conditions persisting.
A weak layer of facets exists near the base of the snowpack. The likelihood of human triggering is low given the layer's depth.
Suspect terrain for human triggering includes steep, shallow, and rocky terrain where the snowpack transitions from thin to thick.
Reports from Monday included a few more storm slab avalanches that were noted for being triggered remotely (from a distance). These ranged from 20-50 cm deep but seem to have shared the same storm interface failure plane, which has been noted as surface hoar and as facets in some of the more prominent reports of touchy conditions from the past few days.
At least one new persistent slab was observed with a 100 cm crown fracture in the western Purcells. Further observations may reveal more activity at this deeper layer in the days to come.
Saturday and Sunday saw an overall increase in wind slab and storm slab activity as the storm touched down in the region. This MIN gives a good sense of the conditions initially at play.
Looking forward, elevations that saw moderate to heavy rain should see avalanche activity drastically reduce with overnight cooling periods. Areas where new surface crust is very thin and especially where it is absent may still harbour upper snowpack instabilities.
Continuing convective flurries will bring light new snow amounts to the region through Tuesday night, adding to about 30-50 cm of recent storm snow. Recent high freezing levels much of this fell as moist heavy snow or rain below about 2000 m, leading to a new melt freeze crust here and below. Expect wind slabs to have formed from southwest winds higher up where snow was light enough to be transported.
On southerly aspects at treeline, there is another widespread crust now buried 30 to 50 cm deep. On north-facing slopes at treeline and above this layer may exist instead as faceted snow or surface hoar in sheltered areas. A second surface hoar layer found closer to 60 cm deep has been reactive to human triggering primarily in the Selkirks on northeasterly slopes from 1700 m to 2100 m. Wednesday was the last day that there was notable activity on this layer but this may have changed during the storm.
The mid-snowpack is generally strong but the lower snowpack is a different story. The November facets are still prominent at the base of the snowpack. This layer remains a concern in rocky, shallow, or thin to thick snowpack areas at treeline and above.
Tuesday night
Cloudy with continuing flurries bringing a trace to 10 cm of new snow. Light southwest winds.
Wednesday
Mainly cloudy with scattered flurries bringing a trace of new snow. Light west winds shifting northwest. Treeline high temperatures around -3 with freezing levels to 1400-1600 m.
Thursday
Mainly sunny. Light west or southwest winds. Treeline high temperatures around -1 with freezing levels to 1400-1600 m.
Friday
Cloudy with isolated flurries bringing a trace to 5 cm of new snow. Light southwest winds. Treeline high temperatures around 0 with freezing levels to around 1700 m.
More details can be found in the Mountain Weather Forecast.
