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Archived

Avalanche Forecast

Dec 20th, 2015–Dec 21st, 2015
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: South Coast.

Forecast new snow and wind continue to build storm slabs at all elevations. Deep pockets of wind transported snow may be easy to trigger at higher elevations.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Another pulse of Pacific moisture should bring 5-10 cm by Monday morning combined with moderate southwest winds and freezing levels down to about 300 metres. Light winds and periods of convective flurries during the day Monday. Light snow on Tuesday with westerly winds and freezing levels briefly rising to 500 metres. Wednesday continued light snow and moderate southwest winds.

Avalanche Summary

Skiers triggerd a thin ( 20 cm deep) storm slab on a poorly supported  east aspect in the Coquihalla that suggests that wider fracture propagations are possible.

Snowpack Summary

Up to 20 cm overnight in the south of the region and closer to 15 in the north. Variable winds across the region, with reports of strong southwest forming soft slabs in the south, and some social media accounts of unconsolidated snow and light winds in the north around Steep Creek. I suspect storm slabs and weak new cornices developed at higher elevations across the region. There is now 20-40 cm above the surface hoar layer that was reported to be buried on December 17th (151217 SH). There may be a thin sun crust on southerly aspects in the Coquihalla beneath the recent storm snow. Incremental loading like this, with consistent cool temperatures can make it difficult to forecast when the storm slab will become cohesive and possibly reactive above any weak layers or combination of smooth sliding surface and weak layer. There is not a lot of load yet if you look at the mm of water equivalent; only about 25 mm for the 40-50 cm that has fallen, but it is still developing with each new snow fall.

Avalanche Problems

Storm Slabs

Storm slabs may be deep at higher elevations where they have been transported by the wind into deep pockets. Watch for slabs developing at all elevations if the storm snow settles and becomes more cohesive.
Avoid travelling in areas that have been reverse loaded by winds.>Avoid avalanche terrain during periods of heavy loading from new snow and wind.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 3

Cornices

New cornice growth may be weak and fall off naturally or be triggered by continued loading from new snow and wind.
Give cornices a wide berth when travelling on or below ridges.>Extra caution needed around cornices with current conditions.>

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 3