Avalanche Forecast
Regions: South Coast Inland.
Wind slabs are the main concern in the region, but we have persistent weak layers sitting at triggerable depths as well. Our confidence in their strength isn't iron-clad and spatial variability is a factor. Check out our Forecasters' Blog before planning your line this weekend.
Confidence
Moderate -
Weather Forecast
Thursday night: Clear. Light to moderate east or northeast winds.
Friday: Sunny. Light to moderate east winds. Alpine high temperatures around -19.
Saturday: Cloudy with isolated flurries bringing a trace to 5 cm new snow, mainly in the south of the region, easing overnight. Light to moderate east or southeast winds. Alpine high temperatures around -12.
Sunday: Cloudy with isolated flurries and a trace of new snow. Light south winds. Alpine high temperatures around -9.
Avalanche Summary
Snowfall focused in the Coquihalla zone resulted in heightened storm slab activity over the weekend. Several natural and skier triggered avalanches averaging size 1-2 were reported. These occurred mostly on south aspects where a reactive storm slab layer formed just above a slippery crust. This reactivity has since abated. A recent (similar timing to the above) widespread natural avalanche cycle in the Mt. Outram area may have been associated with this layer.
A notable size 3 (very large) persistent slab was remotely triggered (from a distance) by a group of skiers in the McGillivray Pass area on Monday. This occurred on a southwest aspect at 2400 metres. It was described as a hard wind slab formed over our facet layer from late January.
Recent wind slab formations are a concern throughout the region, with shooting cracks noted in windblown surface snow in the Coquihalla on Wednesday as well as a another, smaller (size 1), remote-triggered wind slab reported on 1950 m north aspect in the McGillivray area. The latter failed on our more recent (Feb 4) surface hoar layer.
Snowpack Summary
A stormy period from 4 to 8 February dropped approximately 60 cm of new snow in the Coquihalla, 40 cm near Allison Pass and 20 cm in the north of the region. This snow is likely quite slowly forming bonds with a crust on solar aspects, and possibly surface hoar on sheltered, shaded slopes. A number of avalanches were triggered on preserved large stellar grains just above this layer in the Coquihalla on Sunday. Snowpack tests on Wednesday revealed reactivity at this stellar grain interface has since become more resistant.
An earlier persistent weak layer that was buried around January 24 sits a short way below the recent storm snow. This consists of facets at upper elevations, surface hoar in sheltered areas and a crust on south-facing slopes. An isolated very large avalanche on this layer in the north of the region is discussed in our avalanche summary. It averaged about 100 cm deep in that location. Whumpfs were also recently reported on this layer in the south of the region, indicating this layer might remain a concern there as well.
In the north, a melt-freeze crust from early December may be found 100 to 200 cm deep. Recent reports suggest that this layer is gaining strength and it has been unreactive in recent weeks.
Terrain and Travel
- Carefully evaluate steep lines for wind slabs.
- Watch for areas of hard wind slab on alpine features.
- Be aware of highly variable recent wind loading patterns.
Avalanche Problems
Wind Slabs
Wind slabs may be reactive to human triggers, especially more recent formations and where slabs have formed over a crust (think solar aspects). Increase your caution even more around large, hard wind slabs in alpine areas. these may overlie weak, sugary, faceted snow.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2