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Avalanche Forecast

Archived

Feb 9th, 2021–Feb 10th, 2021

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Coast Inland.

Gather observations and adopt a mindset of initial assessment in the south of the region, where a reactive storm slab problem may still be in play. Don't underestimate wind slabs elsewhere - a very large hard slab was remote triggered by a party in the north of the region Monday.

Confidence

Moderate -

Weather Forecast

Tuesday night: Becoming cloudy with isolated flurries bringing a trace of new snow. Light to moderate northwest winds.

Wednesday: Becoming sunny. Light to moderate north winds. Alpine high temperatures around -22.

Thursday: Sunny. Light northeast winds. Alpine high temperatures around -22.

Friday: A mix of sun and cloud. Light east or southeast winds. Alpine high temperatures around -17.

Avalanche Summary

Recent snowfall focused in the Coquihalla zone has resulted in localized storm slab activity over the weekend. Several natural and skier triggered avalanches averaging size 1-2 have been reported mostly on south aspects where they may be sitting over a slippery crust.

In the north of the region, recent avalanche activity has mainly been limited to skier triggered wind slabs size 1-1.5, however a very 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 a facet layer from late January.

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 likely sits on a slippery crust on solar aspects, and possibly surface hoar elsewhere. Particularly in the Coquihalla, the new snow bonded poorly to these old surfaces and a number of avalanches were triggered on this layer. Looking forward, it is not clear whether the recent snow will bond, or whether this weak interface will remain a concern for several days. Given this uncertainty, a prudent approach would be to assume this is a suspect interface.

An earlier persistent weak layer that was buried around January 24 sits some 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

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Wind slabs may be poorly bonded to the underlying crust.
  • Be careful as you transition into wind affected terrain.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.