Watch for wind slabs forming at higher elevations.
Small wind slabs may trigger larger avalanches on deeply buried weak layers. Continue to avoid wind affected, thin and rocky terrain.
Wind slabs may exist where dry snow is available for transport by southwest winds. Watch for reactivity on north and east facing slopes near ridgelines.
Small wind slabs have the potential to step down to deeper weaknesses within the snowpack.
Lingering weak layers are present at all elevations and on various aspects. Of most concern is a layer of surface hoar most prominent near Invermere and the Toby Creek drainage, 40-70 cm deep. This layer has shown reactivity in testing on north and east facing slopes, where wind loading may increase likelihood of triggering an avalanche on this layer.
The base of the snowpack remains very weak. Very large human-triggered avalanches are possible at treeline and above. Avoid thin, rocky start zones and shallow areas with variable snowpack depths. Weak layers are most triggerable here as they sit closer to the surface of the snowpack.
Reduce your exposure to large slopes overhead during intense snowfall or wind. Deep persistent avalanches are challenging to predict. This layer can suddenly become active again, typically when there is rapid change or stress to the snowpack - sudden warming, heavy snow or rainfall, or heavy loads eg. cornice fall.
On Thursday a natural cornice fall (from strong sunshine) triggered a loose dry avalanche to size 2. Several naturally triggered ice falls have also been reported this week - while they have not triggered avalanches they are hazardous on their own.
No activity on the deeply buried weak layers has been reported this week. However thin and rocky terrain features in the upper treeline and alpine should still be avoided.
Light accumulations of storm snow will form deeper deposits on north and east facing slopes at treeline and above. New snow will sit over previous wind affected surfaces at higher elevations on shaded aspects, faceted snow and surface hoar in sheltered areas, and over a melt freeze crust on south facing slopes and at low elevations.
The mid snowpack holds several persistent weak layers that vary throughout the Purcells, including layers of surface hoar in wind-sheltered terrain and sun crusts on south facing slopes. Activity on these layers has tapered off, however a layer of surface hoar around Toby Creek buried up to 70 cm has produced recent test results indicating it is still reactive.
The lower snowpack includes a widespread layer of large, weak facets and or depth hoar crystals. This weak layer has been responsible for a number of very large, destructive avalanches this season, including several last week during warm temperatures and will continue to be a concern for the rest of the season.
Friday Night
Mostly cloudy with flurries delivering up to 5 cm of snow. Moderate southwest wind gusting 50 km/h. Freezing level remains around 500 m overnight.
Saturday
Cloudy with sunny periods possible in the afternoon. Light snowfall brings 5-10 cm for eastern terrain. Western Purcells may see up to 25 cm total. Moderate southwesterly wind gusting 50 km/h. Freezing level rises to 1500 m, alpine highs of -5 °C.
Sunday
A mix of sun and cloud with flurries with trace accumulations. Freezing levels rise to 1300 m with alpine highs of -7 °C. Light west winds.
Monday
Mostly cloudy. Light westerly winds. Freezing levels rise around 1000 m.
More details can be found in the Mountain Weather Forecast.
