Avalanche Forecast
Issued: Dec 16th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs.
cmortenson,
Avalanche Canada
A stormy night makes for increased avalanche hazard. Another 30-50cm of snow is forecast Wednesday night above 1000m (rain at lower elevations) & strong south winds will create dangerous avalanche conditions. Stick to cautious terrain, avoid steep slopes & any overhead danger.
Summary
Confidence
Weather Forecast
Wave after wave of frontal systems will bring more precipitation as they move through the South Coastal ranges through the weekend. Wednesday night is forecast to see heavy amounts of rain and snow. Then a brief ridge of high pressure provides cloudy but dry weather on Thursday ahead of a stronger r wave on precipitation for Friday. On Saturday a warmer and even stronger wave of precipitation will arrive.
Wednesday Night: Precipitation with accumulations of 30-50cm snow (30-50mm rain), moderate west ridgetop wind, alpine low 1 C, freezing level 1000 m.
Thursday: Cloudy with scattered flurries, trace to 5cm accumulation, moderate northwest wind, alpine high 2 C & low-2C, freezing level 1400 m.
Friday: Heavy Snow, accumulation of 20-50cm new snow, moderate south winds gusting strong, alpine high 1 C & low-2C, freezing level 1400 m.
Saturday: Heavy snow and rain with accumulation of 30-60cm snow (30-60mm rain), strong to extreme southwest ridgetop wind, alpine low 0C & alpine high +5C, freezing level rising to 2000m.
Avalanche Summary
Limited observations from Wednesday have been reported, however natural human triggered avalanches are likely with the recent strong to extreme southwesterly winds and new snow.
Heightened avalanche conditions will persist as heavy amounts of snow fall throughout the weekend. In areas where snow becomes wet and rain soaked be on the look out for loose snow avalanches and wet slides being triggered on buried crusts.
Have you been out and about in the mountains? If so please submit your observations to the Mountain Information Network (MIN). It doesn't have to be technical - photos are especially helpful! Thank you so much for all the great MINs submitted so far!
Snowpack Summary
Wet and stormy weather continues to bring a mix of rain and snow to the North Shore mountains. Recent storms delivered 40-60cm of snow, which has settled rapidly with warm temperatures. Another 25-50cm is forecast overnight Wednesday at locations above 1000m. If this significant precipitation arrives, it will bring storm totals the past week to 65-1100 cm.
There are a few melt freeze crusts that we are watching that have shown up as weak layers in test pits.
Below treeline snowfall amounts are approaching threshold for avalanches to occur.
We have very little data and a lot of uncertainty around alpine conditions in the region. If you go out in the mountains, please let us know what you see via the Mountain Information Network (MIN).
Terrain and Travel
- Minimize exposure during periods of heavy loading from new snow and wind.
- Keep in mind the crust offers an excellent bed surface for avalanches.
- As the storm slab problem gets trickier, the easy solution is to choose more conservative terrain.
- The more the snow feels like a slurpy, the more likely loose wet avalanches will become.
Problems
Storm Slabs
Additional 30-50 cm recent new snow in the North Shore mountains overnight Wednesday will bring total snow fall amounts in the past week to 60-110 cm. This snow has shown reactivity on a variety of sliding layers, most notably a series of crusts from melt freeze or rain events. New snow will be particularly reactive where recent southwestern winds have created wind loaded pockets just below ridge crests and roll-overs.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 17th, 2020 4:00PM
