Avalanche Canada cgarritty, Avalanche Canada

Sea to Sky Avalanche Forecast

Jan 15th, 2020 4:00PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is high. Known problems include Storm Slabs and Deep Persistent Slabs.

Continuing snowfall and extreme winds will maintain dangerous avalanche conditions in the Sea to Sky, particularly in areas closest to the coast. Natural avalanche activity is expected to become widespread in wind-exposed areas.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Wednesday night: Cloudy with heavy snowfall bringing 30-50 cm of new snow. Strong to extreme south winds.

Thursday: Cloudy with continuing flurries bringing 15-25 cm of new snow. Strong southwest winds, easing over the day. Alpine temperatures around -13.

Friday: Mainly cloudy with flurries beginning overnight. Light south or southeast winds. Alpine temperatures around -12.

Saturday: Cloudy with continuing snowfall bringing 15-25 cm of new snow. Strong south winds. Alpine high temperatures around -5.

Avalanche Summary

Reports from the Whistler area on Tuesday showed small (size 1) pockets of wind slab continuing to react to ski cutting, with crown fractures 20-30 cm deep.

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.

On Sunday the top 30 to 40 cm of recent snow was sensitive to control work producing avalanches up to size 2 on all aspects.

Looking forward, another round of potentially heavy snowfall paired with extreme winds will ramp up avalanche danger in the region again for Thursday. Touchy storm slabs are expected to form quickly and either fail naturally or be very reactive to human triggering.

Snowpack Summary

45-70 cm of new snow is expected to accumulate in the region by the end of Thursday under the influence of strong to extreme south winds. This will bury previously wind-affected surfaces in exposed areas at all elevations and soft, low density snow in sheltered areas.

The new snow will add to about a meter of storm snow has fallen in the last week. In exposed areas, this snow has seen substantial wind from both the south and the north.

A weak layer of snow known as the late December surface hoar is currently 70 to 200+ cm below the snow surface. Tests from snow profiles show this interface likely remains sensitive to human triggering, but not everywhere. Problem locations are places where the snowpack goes from thick to thin, steep unsupported slopes and around rock outcroppings.

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

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.

Problems

Storm Slabs

An icon showing Storm Slabs

Likelihood

Very Likely-Almost Certain

Expected Size

1 - 2

Another round of heavy snowfall is expected to form a widespread new storm slab problem to manage on Thursday. Forecast strong to extreme winds will play a major role in rapidly forming touchy storm slabs. The heaviest accumulations and most dangerous conditions may be focused toward the south of the region. 

Aspects:

All aspects.

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.

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Valid until: Jan 16th, 2020 5:00PM