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Avalanche Forecast

Archived

Dec 18th, 2019–Dec 19th, 2019

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

Regions

South Coast.

It's finally happening. Continued heavy snowfall is in the forecast for Wednesday night. Very dangerous avalanche conditions are expected and travel in higher elevation avalanche terrain is not recommended.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

WEDNESDAY NIGHT: Continuing heavy snow, bringing 30 cm or more new snow by morning. Strong south winds.

THURSDAY: Continuing flurries bringing 10-15 cm of new snow and 2-day snow totals to 50-60 cm. Precipitation increasing and transitioning to wet flurries or rain overnight. Moderate south winds becoming strong overnight. Alpine high temperatures around -2 with freezing level to 1200 metres, increasing to 1700 metres overnight.

FRIDAY: Cloudy with easing flurries bringing approximately 10 cm of new snow. Light to moderate southwest winds. Alpine high temperatures around -1 with freezing levels falling back to 1300 metres.

SATURDAY: Cloudy with isolated flurries and a trace of new snow. Light variable winds. Alpine high temperatures around -3.

Avalanche Summary

We haven't yet received reports of avalanches from the latest snowfall, but expect our most recent accumulations to be sensitive to human triggering and capable of producing large avalanches on Thursday. Anticipate areas where the new snow has been loaded and stiffened by strong winds to be the most reactive.

Snowpack Summary

Heavy snowfall forecast to continue through Wednesday night will bring a substantial layer of new snow to the region for Thursday. 

This time around, the new snow has buried an array of smooth surfaces provided by the 30-50 cm of snow we received last week at treeline and in the alpine. Recent observations show the new snow has buried a weak layer of surface hoar in the North Shore mountains.

Below the new snow, last week's storm snow mainly covers bare ground, smoothing over previous ground roughness. This smoothing effect has given us more widespread planar surfaces for avalanches as new snow accumulates and forms storm slabs.

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.