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Avalanche Forecast

Archived

Jan 16th, 2020–Jan 17th, 2020

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

Regions

South Coast Inland.

Watch for newly formed wind slabs on Friday. These may exist at surprisingly low elevations in areas that saw the most new snow and strongest wind on Thursday. The north of the region is the greatest concern for both of these factors.

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Thursday night: Cloudy with isolated flurries with a trace to 5 cm of new snow. Light to moderate southwest winds.

Friday: Mainly cloudy. Light to moderate southwest winds. Alpine high temperatures around -14.

Saturday: Cloudy with flurries bringing 3-5 cm of new snow, continuing overnight. Light to moderate south winds. Alpine high temperatures around -7, closer to -4 in the south of the region.

Sunday: Cloudy with easing flurries and a trace of new snow. Light to moderate south winds. Alpine high temperatures around -2, closer to 0 in the south of the region.

Avalanche Summary

Reports from the region have been limited during the cold snap, however a MIN from Tuesday describes winds actively forming new slabs in the Duffey area. Similar conditions were observed in the Coquihalla area:

On Monday small wind and storm slabs to size 1.5 were observed in the recent storm snow. Interesting to note that wind slabs were observed in open treeline features which speaks to the widespread nature of Sunday's north wind event.

On Saturday, the snowpack was reactive to explosive triggers. Some avalanches stepped down to a feathery surface hoar layer buried 50-60 cm deep.

Last Thursday, explosive control work produced a size 2 avalanche off the Duffey Lake road that released on the mid November facet/crust layer.

Snowpack Summary

About 20 cm of new snow accumulated in the north of the region during the midweek storm, with only a trace of new snow in the south of the region. Moderate to strong winds redistributed loose surface snow, (new snow in the north, old snow in the south) into new wind slabs on Wednesday night and Thursday. 

This new snow and new wind slab is layered above an older layer of wind-affected snow from the recent arctic outflow event.

A deep persistent weak layer remains a serious concern at the bottom of the snowpack in the northern half of the region (e.g., Duffey, Hurley). It's made up of sugary faceted grains and a hard melt-freeze crust. This layer is most likely to be triggered in thin, rocky features where it exists closer to triggering forces on the surface.

There are currently no concerns about deep weaknesses in the snowpack near Coquihalla summit and elsewhere in the south of the region.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Keep your guard up at lower elevations. Wind slab formation has been extensive.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.