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Avalanche Forecast

Archived

Dec 22nd, 2020–Dec 23rd, 2020

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

Regions

South Coast Inland.

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.

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. 

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

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.