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Avalanche Forecast

Archived

Nov 22nd, 2019–Nov 23rd, 2019

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

Regions

Northwest Coastal.

"There's something happenin' here, but what it is ain't exactly clear."

 

There are no observations from the ongoing storm impacting the region, but it's safe to assume that serious avalanche danger exists at elevations where precipitation is falling as snow instead of rain.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Friday night: Precipitation easing off with an additional 5-10 cm of snow accumulating above about 1200 metres. Strong west winds easing overnight.

Saturday: Cloudy with another storm pulse bringing 20-30 cm of new snow to high alpine areas. Moderate to heavy rain below about 1500 metres. Strong to extreme southwest winds. Alpine high temperatures around 0 to +2 with freezing levels rising from 1100 to 1900 metres over the day.

Sunday: Cloudy with isolated flurries and a trace of new snow. New snow totals of up to 60 cm at highest alpine elevations. Light to moderate southwest winds. Alpine high temperatures around -5 with freezing levels to 800 metres.

Monday: Mainly cloudy. Light west winds. Alpine high temperatures around -7 with freezing levels to 500 metres.

Avalanche Summary

Observations from Friday's storm have yet to come in, but it is expected that the significant load of new snow (along with strong winds) in the alpine has been promoting natural storm slab avalanches in areas where the new snow is accumulating over previous smooth snow cover. Looking forward, a second storm pulse on Saturday is expected to continue this type of activity.

Snowpack Summary

Heavy rain over Friday is expected to have eroded much of the patchy snow cover that existed below the alpine while adding 30-40 cm of new snow to alpine areas, effectively doubling snowpack depths at these higher elevations. Beyond the sheer quantity of new load, the bond between the new snow and the melt-freeze crust capping our older storm snow is expected to be poor, particularly in areas that did not experience rain in advance of the recent snowfall (higher elevations). 

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.