Avalanche Canada cgarritty, Avalanche Canada

Sea to Sky Avalanche Forecast

Jan 16th, 2020 4:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Wind Slabs and Deep Persistent Slabs.

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.

Summary

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

An icon showing Wind Slabs

Likelihood

Likely

Expected Size

1 - 2

Our most recent 30-40 cm of new snow is expected to form an improving bond with the old surface, however areas where winds have created thicker, more reactive slabs remain a concern. Recent strong to extreme winds have scoured many upper elevations and wind-loaded lower elevation features.

Aspects:

North, North East, East, West, North West.

Elevations:

All elevations.

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

Likelihood

Unlikely-Possible

Expected Size

2.5 - 3.5

The weak snowpack base still exists in much of the region. Although the likelihood of triggering this layer has substantially decreased, the consequence triggering an avalanche on this layer would be severe. Its most likely trigger points will be in steep, shallow, rocky areas where this layer exists closer to triggering forces on the surface.

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Valid until: Jan 17th, 2020 5:00PM