Extensive reports of heavy sluffing and touchy storm slabs have resulted from the storm, even with limited observations and conservative terrain selection. Stick to low consequence slopes while the new snow settles and put your guard way up if the sun pokes out on Tuesday. This is most likely in the north of the region.
In higher snowfall parts of the region like the Monashees, deep accumulations of new snow that haven't formed into a slab are likely to create large sluffs with rider traffic in steep areas.
With 20-80 cm of new snow (greatest in the Monashees, least in the Selkirks) from the weekend overlying weak grains like faceted snow and small surface hoar, we may see storm slab reactivity persist for longer than usual.
What's more certain is that large wind-loaded slabs perched on leeward (north-facing) terrain will be primed for human triggering.
A weak layer of facets exists near the base of the snowpack. The likelihood of human triggering is low given the layer's deep burial depth, but storm slab avalanches in motion have the potential to step down. Suspect terrain for human triggering includes steep, thin, shallow, and rocky terrain, which is often found near ridgelines.
It was a busy day for avalanche activity in the region with almost all operators reporting some variation of the theme of a natural and skier-triggered avalanche cycle as 40-70 cm of new snow settled into touchy storm slabs in some areas and produced powerful dry loose releases where slabs hadn't quite formed. Savvy terrain use kept most releases small, however large audible avalanches are peppered throughout Sunday's reports.
Clear skies last week allowed for observations of many deep persistent slab avalanches as well as explosive control missions, which produced large to very large (size 2 to 3.5) avalanches. They were on all aspects and between 2200 m and 2800 m in elevation. Although many of the avalanches occurred in unrideable terrain, they are evidence that the weak basal snowpack is still triggerable. Riders should continue to avoid thin snowpack areas, which are often found near ridgelines.
Looking forward, storm slabs from the weekend may remain sensitive to human triggering a bit longer than usual, owing to the weak faceted snow they overlie. Otherwise we expect surface instabilities to gradually become more focused toward wind loaded areas.
Stormy conditions over the weekend brought up to about 40-80 cm of new snow to the Monashees, closer to 20-50 cm in the Selkirks, along with strong southwest wind. The new snow buried an interface from the recent cold period which includes faceted (sugary) surface snow, small surface hoar in sheltered areas, and widespread heavy wind effect and wind slabs in exposed terrain from recent northeast winds. Below this interface is 20-50 cm of older storm snow from the beginning of last week.
Around 100 to 130 cm of snow may now rest on a small layer of surface hoar crystals that was buried mid-February. This layer is most likely found around treeline elevations in areas sheltered from the wind. This layer generally appears to be dormant now but could still be capable of producing avalanches in isolated areas. The remainder of the mid-snowpack is generally strong.
A layer of large and weak facets that formed in November is deeply buried, found near the base of the snowpack. The likelihood of human triggering this layer is currently low given its depth. However, it is still best to avoid steep, thin, rocky slopes near ridges at alpine and upper treeline elevations.
Monday night
Mainly cloudy with isolated flurries. Light southeast winds.
Tuesday
Mainly cloudy with isolated flurries. Light east or southeast winds. Treeline high temperatures around -8 °C.
Wednesday
Cloudy with isolated flurries, increasing overnight. Light west winds shifting southwest and increasing. Treeline high temperatures around -8.
Thursday
Cloudy with continuing snowfall bringing 10-25 cm of new snow, greatest in the north of the region. Moderate southwest winds. Treeline high temperatures around -7.
More details can be found in the Mountain Weather Forecast.
