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Avalanche Forecast

Archived

Feb 20th, 2021–Feb 21st, 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 avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Sea To Sky.

New snow, wind, and rain will create very dangerous avalanches conditions across many parts of the region. Stick to flat and low angle slopes away from avalanche terrain.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

A warm front will bring intense weather to coastal parts of the region and moderate snowfall further inland.

SATURDAY NIGHT: 5-15 cm of snow for most parts of the region but closer to 20 cm near the coast, strong southwest wind, freezing level climbing to 1100 m by the morning with treeline temperatures around -4 C.

SUNDAY: 15-25 cm of snow throughout the day, strong to extreme southwest wind, freezing level climbing to 1400 m with treeline temperatures reaching -2 C.

MONDAY: Another 20-30 cm of snow, moderate southwest wind with strong gusts, treeline temperatures drop to -6 C.

TUESDAY: Mix of sun and cloud, light northwest wind, treeline temperatures around -6 C.

Avalanche Summary

The main story on Sunday will be new storm and wind slabs with the incoming storm.

A small 15 cm storm on Friday resulted in in several small (size 1) human triggered storm and wind slabs, with explosive control producing some larger (size 2) avalanches on bigger terrain features.

There was some notable avalanche activity a week ago after a bout of northerly winds formed wind slabs in unusual places (eg. south, southeast, and southwest facing slopes). On Feb 11, two skiers were caught in a natural wind slab avalanche in a couloir on Mamquam Mountain, resulting in serious injuries. On Feb 12, a fatal avalanche was triggered by skiers at 2200 m on a west-facing slope on Phalanx Mountain (a size 2.5 wind slab). On Feb 12, another fatal avalanche was triggered by skiers at 1700 m on a treed southwest-facing slope in the Brandywine valley (a size 1 wind slab). See the incident reports here and here for details. These old wind slabs have decreased in reactivity over the past the week, however may still present as a problem with the stress of new snow and wind.

Snowpack Summary

Forecast snowfall amounts are variable across the region with 40 cm expected in coastal areas like Squamish and the Sunshine Coast and closer to 20 cm further inland near Whistler and Pemberton. The new snow and wind will form reactive slabs at all elevations, while rain could be expected up to 1400 m.

The new snow adds to 15 cm of recent snow sitting above a potentially reactive interface consisting of surface hoar layer at treeline, a crust below 1800 m, sun crusts on steep south slopes, and faceted surfaces in the alpine. These interfaces could be failure layers during the storm. 

A lingering persistent weak layer from late January is 80-120 cm deep and consists of facets at upper elevations and surface hoar in sheltered areas. Although this structure is suspect, we have no recent reports of avalanches on this layer.

Terrain and Travel

  • Minimize exposure during periods of heavy loading from new snow, wind or rain.
  • Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time.
  • Keep in mind that wet avalanches can be destructive due to their high density.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.