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Avalanche Forecast

Archived

Jan 5th, 2021–Jan 6th, 2021

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

Regions

South Coast Inland.

Forecast snowfall amounts in the south of the region near Coquihalla pass are uncertain Tuesday night. If overnight snowfall exceeds 25 cm, expect the avalanche danger to be HIGH.

Confidence

Low - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

Tuesday Night: Heavy snowfall above 1100m in the Coquihalla area with accumulations of 20-40 cm. Snow accumulation in the north of the region expected to be 5-15 cm. Strong southwest wind, alpine high -2, freezing level 1300 m.

Wednesday: Mainly cloudy, southwest wind easing to light, alpine high -2, freezing level 1300 m.

Thursday: Sun and cloud, light t moderate south wind, alpine high -3, freezing level 1100 m.

Friday night: Flurries, up to 5 cm, moderate to strong southwest wind, freezing level 700 m.

Avalanche Summary

No avalanches were reported Monday and Tuesday. Over the weekend, a large natural storm slab avalanche cycle was observed up to size 3 in much of the region and up to size 4 near Pemberton.

Persistent slab avalanche activity has tapered significantly since the cycle early last week, but persistent slabs size 2-2.5 were still triggerable by explosives on weekend.

Snowpack Summary

Over 70 cm of recent snow has seen extensive wind affect at upper elevations, with scoured windward aspects, wind slabs in lee features and growing cornices at ridgetop. In sheltered areas below treeline, recent snow may be sitting on surface hoar. 

A melt-freeze crust from early December is found around 80 to 180 cm deep in the snowpack. This crust may have surface hoar or sugary faceted grains sitting above it. This persistent weak layer is most prevalent in the north (e.g., Duffey Lake, Hurley) and found to a lesser extent in the south of the region.

The remainder of the snowpack is generally well settled.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Start with conservative lines and watch for clues of instability.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

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.