Continued snowfall, wind, and warming are creating dangerous avalanche conditions. Reactive storm slabs sit above a complex snowpack, increasing the likelihood of triggering large and destructive avalanches.
Numerous problematic weak layers exist in the top meter of the snowpack, at prime depths for human triggering. Be especially cautious around steep openings within and near treeline elevations.
This week's 40-70 cm of storm snow combined with the strong southwesterly wind and warming temperatures will form reactive storm slabs, especially on leeward slopes that may see more loading from the wind. Dry loose avalanches and sluffing will occur from steep terrain.
Keep in mind that storm slabs have the potential to step down to deeper weak layers, resulting in large and consequential avalanches.
A layer of large and weak facets sits near the base of the snowpack. This layer continues to produce very large avalanches that can travel far. Riders are most likely to trigger an avalanche on this layer in steep, shallow terrain, or by triggering a smaller avalanche that could step down to this layer.
On Wednesday, most reports came in as dry loose avalanches and sluffing up to size 1. Some areas in the Monashees did see more reactivity in the recent storm snow up to size 1.5. These were easily rider triggered and failed naturally.
As the wind picked up and temperatures rose on Thursday, numerous natural and human-triggered storm and wind slabs were observed throughout the region up to size 2.5. One natural persistent slab avalanche (size 2.5) was observed in the Valhalla mountains. It initiated as a wind slab, stepped down to mid-snowpack weak layers, and then gouged to the basal facets, stepping down to the ground.
Last weekend, various deep persistent slab avalanches were also triggered naturally, being large to very large (size 2 to 4). The avalanches occurred on all aspects between 2400 and 2800 m.
High-consequence avalanche activity is ongoing for several weeks now. Most of the avalanches over the past week were released between 1800 and 2800 m, on all aspects.
Your best defense is to stay diligent in choosing low-consequence terrain away from overhead exposure.
See more on the potential of triggering deeper weak layers in Forecasters' Blog.
Up to 25 cm of overnight snowfall will be accompanied by moderate to strong southwesterly wind. This new snow brings this week's storm snow totals to 40-70 cm. This storm snow sits above a plethora of old snow surfaces including previously wind-affected snow at upper elevations, a sun crust on steep solar aspects, faceted snow, and surface hoar crystals in wind-sheltered terrain.
Below the recent snow is a crust that extends up to 1800 m in the northern part of the region and up to 2000 m further south. This crust is buried about 40 to 100 cm deep and may host small facets on the crust.
Deeper in the snowpack two layers of surface hoar which formed in early January are 60 to 120 cm deep. These weak layers are still on our radar, although snowpack tests are starting to indicate they may be slowly strengthening.
Large and weak facets from November are near the base of the snowpack, which continue to produce very large avalanches in the region, as described in the Avalanche Summary.
Friday night's storm snow accumulation will vary significantly across the region. The Monashee mountains are looking like the hotspot, but there is uncertainty due to the convective nature of this storm.
Friday night
Mainly cloudy with periods of snow, heavy at times with accumulation varying from 5 to 25 cm. Alpine temperatures drop to a low of -6 °C. Ridge wind southwest 25 km/h gusting to 60 km/h. Freezing level 400 to 1000 meters.
Saturday
Cloudy with sunny periods and isolated flurries, with up to 5 cm of accumulation. Alpine temperatures reach a high of -4 °C. Mostly light ridge wind occasionally gusting to 35 km/h from the southwest. Freezing level 1400 meters.
Sunday
Cloudy with snowfall, 5 to 15 cm of accumulation. Alpine temperatures reach a high of -4 °C. Ridge wind west 20 km/h to 60 km/h. Freezing level 1300 meters.
Monday
A mix of sun and cloud with isolated flurries. Alpine temperatures reach a high of -5 °C. Ridge wind southwest 20 km/h gusting to 50 km/h. Freezing level 1300 meters.
More details can be found in the Mountain Weather Forecast.
