Avalanche Forecast

Archived

Jan 6th, 2021–Jan 7th, 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 unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Coast Inland.

Tuesday night's storm brought 15-20 cm of new snow combined with moderate to strong wind. As a result wind slabs at upper elevations are the main concern on Thursday.

Confidence

Moderate - Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Wednesday Night: Mainly cloudy, light to moderate southwest wind, alpine high -5.

Thursday: Mainly cloudy with sunny breaks, light southeast wind, alpine high -3 freezing level 900m.

Friday: Flurries, 3-5 cm, moderate southerly wind, alpine high -3, freezing level 1000 m.

Saturday: Mainly cloudy with sunny breaks, light south wind, alpine high -3, freezing level 1000 m.

Avalanche Summary

Reports from Wednesday include a human triggered size 2 storm slab avalanche at 2000 m on a north aspect in the Duffy Lake area. As well a few natural size 1-1.5 naturally triggered windslabs in the alpine. On Tuesday there was a size 2 persistent slab avalanche reported on Tuesday on Joffre Shoulder. See this MIN report for more details.

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 in the past week 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.

Terrain and Travel

Be careful as you transition into wind affected terrain.
Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.