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Avalanche Forecast

Archived

Jan 16th, 2020–Jan 17th, 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 and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.

Regions

Sea To Sky.

Winds have had a big impact on our recent snow, scouring many exposed areas and redistributing snow into lower elevation features. Watch for recently formed wind slabs in unexpected locations on Friday.

Confidence

Moderate -

Weather Forecast

Thursday night: Cloudy with easing flurries bringing about 5 cm of new snow. Moderate southwest winds, easing.

Friday: Mainly cloudy with flurries beginning overnight. Light southwest winds. Alpine temperatures around -13.

Saturday: Cloudy with continuing snowfall bringing 15-25 cm of new snow, continuing overnight. Moderate to strong south or southeast winds. Alpine high temperatures around -5.

Sunday: Cloudy with easing flurries bringing 10-20 cm of new snow and 2-day snow totals to 60-90 cm. Moderate south winds, easing over the day. Alpine temperatures reaching -1 as freezing levels rise to 1700 metres and continue to rise overnight.

Avalanche Summary

Reports from the Whistler area on Tuesday and Wednesday showed small (size 1-1.5) pockets of wind slab continuing to react to ski cutting, with crown fractures 20-40 cm deep. Explosives control in the same area yielded larger (size 2) results on Wednesday. Reports from Thursday will likely show an increasing trend of activity owing to a renewed supply of snow and strong to extreme winds.

On Monday avalanche activity was tempered by very cold temperatures. Control work produced avalanches to size 1.5 in alpine features with crown depths up to 20 cm.

Looking forward, our most recent snow is expected to settle and form a strengthening bond with the surface, while surface instabilities become increasingly focused toward wind-loaded areas. Another storm arrives Friday night.

Snowpack Summary

About 35 cm of new snow accumulated in the region by the end of Thursday under an initial influence of strong to extreme south winds. The new snow buried previously wind-affected surfaces in exposed areas at all elevations and soft, low density snow in sheltered areas.

The new snow adds to about a meter of storm snow that has fallen in the last week. In exposed areas, this previous snow also saw substantial wind from both the south and the north.

Professionals in the region are continuing to track a pair of weak surface hoar layers from mid and late December. Now 70 to 160 cm below the snow surface, these layers are giving increasingly stubborn results in snowpack tests but may remain sensitive to human triggering in places where the snowpack goes from thick to thin, steep unsupported slopes, and around sheltered shallow, rocky start zones.

The beginning of the season had less precipitation than usual, which led to a layer of sugary faceted grains as well as a hard melt-freeze crust near the base of the snowpack. In a more seasonally normal winter we wouldn't be thinking about this interface, but it has produced large, destructive natural avalanches as recently as January 11th.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Keep your guard up at lower elevations. Wind slab formation has been extensive.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.

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.