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Avalanche Forecast

Archived

Dec 19th, 2019–Dec 20th, 2019

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Coast Inland.

Substantial amounts of snow may accumulate Thursday night into Friday. The snow will load a buried weak layer and may trigger an avalanche cycle. Best to avoid avalanche terrain on Friday and give the snowpack time to stabilize.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

THURSDAY NIGHT: Cloudy with heavy snowfall, accumulation 30 to 50 cm, strong to extreme southwest wind, alpine temperature -4 C, freezing level 1200 m.

FRIDAY: Cloudy with snowfall, accumulation 5 cm in the north of the region and 30 cm in the south of the region, moderate to strong southwest wind, alpine temperature -5 C, freezing level 1100 m.

SATURDAY: Cloudy with snowfall, accumulation 5 to 10 cm, moderate southwest wind, alpine temperature -6 C, freezing level 900 m.

SUNDAY: Mix of sun and cloud, light south wind, alpine temperature -6 C, freezing level 800 m.

Avalanche Summary

A natural avalanche cycle is possible Thursday night into Friday for areas that receive snowfall amounts of 30 cm or more. It will be best to avoid avalanche terrain during periods of heavy snowfall.

Snowpack Summary

Around 30 to 80 cm of snow is expected to accumulate across the region by Friday afternoon, with the most in the south of the region (e.g., Coquihalla, Allison Pass). This snow will likely be very touchy and may produce both natural and skier-triggered avalanches Thursday night into Friday.

In the north of the region, the snow will load a weak layer of sugary faceted grains and hard melt-freeze crust buried mid-November, which is a recipe for large and destructive avalanches and a problem that may persist for weeks to months.

In the south of the region, the snow will load a weak layer of feathery surface hoar buried about 60 to 90 cm.

Avalanches triggered in the storm snow could step down to these buried weak layers, producing large and destructive avalanches.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.