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Avalanche Forecast

Archived

Nov 26th, 2021–Nov 27th, 2021

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Sea To Sky.

Rain and heavy snow on Saturday will increase the avalanche hazard as it accumulates. Avoid exposure to overhead hazards.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather. Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Friday night: Mainly cloudy. Moderate southwest winds.Treeline low temperatures around -4. Freezing level around 900 m.

Saturday: 10-15 cm of heavy snow, another 40-50 cm overnight. Moderate to strong south winds, increasing to extreme at night. Treeline high temperatures reach 0C by late afternoon, as freezing levels climb to 1300 during the day and up to 2200 m overnight.

Sunday: 20-30 cm of heavy snow. Moderate to strong southwest winds. Treeline temperatures dropping from +2 to -1 over the day as freezing levels descend from 2200 meters to 1500 meters.

Monday: Flurries. Light to moderate west winds. Treeline high temperatures around 0. Freezing level around 1500 m.

Avalanche Summary

Friday, large avalanches (size 2.5) have been running on a deeply buried crust/facets combo in Whistler area. With the incoming weather, it is likely to continue Saturday. Few size 1 slabs were also skier-triggered in the alpine during Thursday's storm.

Snowpack Summary

Thursday's storm left about 30 cm of new snow in the Whistler area, along with extreme southwesterly winds. Fresh storms slabs are now present at treeline and in the alpine. Reactive winds slabs are also found on leeward alpine slopes.

The new snow buried mainly wind-affected surfaces, however, surface hoar was observed in the Whistler area earlier this week. As a result, storm slab reactivity may persist in places where new snow buried these weak grains. A thick crust, breakable at treeline and below, is now likely 40-90 cm deep throughout the region. This crust may be found directly at the new snow interface or even at the surface on windward slopes. In the alpine, another crust is now probably around 130-170 cm deep.

Average snow depths at treeline are now likely closer to 120-190 cm; 250+ cm in the alpine. Snowpack depths decrease dramatically below treeline and may still be below threshold for avalanches in some areas. This is changing with each storm pulse we see. Early season hazards such as rocks, stumps, and creeks are still a concern at these lower elevations.

Terrain and Travel

  • Avoid areas with overhead hazard.
  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Choose slopes that are well supported and have limited consequence.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.