Avalanche Forecast
Issued: Dec 22nd, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
mconlan,
Avalanche Canada
A warm-up is forecast, with above-freezing alpine temperatures possible in the south of the region. The recent snow could be touchy to human traffic.
Summary
Confidence
Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.
Weather Forecast
TUESDAY NIGHT: Clear skies, 20 to 40 km/h northwest wind, alpine temperature -6 C.
WEDNESDAY: Mix of sun and cloud, 20 to 40 km/h southwest wind, alpine temperature -3 C, freezing level rising to 2500 m in the south of the region.
THURSDAY: Clear skies, 20 km/h southwest wind, alpine temperature 2 C, freezing level 2500 m.
FRIDAY: Mix of sun and cloud, 20 km/h south wind, alpine temperature -1 C.
Avalanche Summary
We received reports of surprisingly little natural avalanche activity from Monday's storm. However, avalanches were still observed across the region on Monday and Tuesday. Recreationists on Monday found the storm snow to be reactive in the south of the region. Check out these observations, as well as this lyrical gem. In the north, small wind slab avalanches were reactive to riders in steep treeline terrain on Tuesday, generally 20 to 30 cm deep.
A few persistent slab avalanches were also triggered in the north of the region on Monday, near the Hurley. They were triggered by riders and heavy machinery. The slabs were 60 to 90 cm deep and released on the weak layers described in the snowpack summary.
Snowpack Summary
Around 60 cm of snow fell near Coquihalla and Manning Park on Monday and 15 cm accumulated near Duffey Lake. The snow fell with northerly wind in the north and north to southwest wind in the south. Storm and wind slabs may take a few days to bond to the snowpack.Â
A hard melt-freeze crust from early December is found around 40 to 120 cm deep in the snowpack. This crust may have weak layers above it, consisting of feathery surface hoar or sugary faceted grains. These weak layers do not appear to be prevalent in the south of the region. The snowpack should be treated as suspect anywhere you find either surface hoar or faceted grains above the crust.
The remainder of the snowpack is well-settled in the south of the region. In the north, another melt-freeze crust with associated faceted grains around it may be found near the ground. Without evidence of recent avalanche activity, the layer appears to be inactive at this time.
Terrain and Travel
- Storm slabs in motion may step down to deeper layers resulting in large avalanches.
- Give the new snow several days to settle and stabilize before pushing into bigger terrain.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
Problems
Storm Slabs
Over 60 cm of snow accumulated in the south of the region and over 15 cm in the north on Monday. A warming trend on Wednesday may promote cohesion of this storm snow and for it to remain reactive to human traffic. Up high, wind slabs are likely to be found adjacent to ridges. The wind direction has varied, so slabs may be found on all aspects.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
Weak layers of surface hoar and/or faceted grains may be found above a hard melt-freeze crust. Where these weak layers exist, they are at a prime depth for humans to trigger them. Large avalanches have recently been triggered on these layers in the north of the region. Recent reports suggest the weak layers may be less prevalent in the south of the region, but they may still exist in localized pockets.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 23rd, 2020 4:00PM
