Avalanche Forecast

Issued: Feb 21st, 2021 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 Persistent Slabs.

Avalanche Canada mconlan, Avalanche Canada

An avalanche cycle may continue into Monday as more snow and strong wind are expected. Travel in avalanche terrain is not recommended.

Summary

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

SUNDAY NIGHT: Cloudy with snowfall, accumulation 5 to 15 cm, 60 km/h west wind, alpine temperature -5 C, freezing level 700 m.

MONDAY: Cloudy with snowfall, accumulation 10 to 20 cm, 40 to 60 km/h northwest wind, alpine temperature -6 C, freezing level 500 m.

TUESDAY: Cloudy with snowfall and afternoon clearing, accumulation 5 to 15 cm, 40 km/h northwest wind, alpine temperature -8 C.

WEDNESDAY: Increasing clouds, 30 km/h southwest wind, alpine temperature -8 C.

Avalanche Summary

A natural avalanche cycle has likely occurred across the region from periods of rapid snow and rain accumulation. Many large storm slab avalanches were reported, although we may not see the evidence of the cycle until the skies clear.

Similar avalanche activity may continue into Monday as more snow and strong wind are forecast.

Snowpack Summary

The region has seen upwards of 100 cm of snow accumulation over the weekend above around 800 m with associated strong south to southwest wind. Storm and wind slab avalanches likely developed rapidly during the storm and a natural avalanche cycle likely occurred at all elevations from rapid snow and rain accumulation. Another 20 to 40 cm of snow may accumulate Sunday night and Monday, with strong west to northwest wind; the avalanche cycle may continue!

All of this snow may not bond well to old surfaces, which may include:

  • Weak and feathery surface hoar in sheltered areas, with the most suspect elevation bands being lower alpine, treeline, and within openings below treeline;
  • A melt-freeze crust found below treeline, particularly on southerly aspects;
  • A 20 to 40 cm thick layer of sugary faceted grains that developed during cold periods; and/or
  • Hard wind-affected snow, particularly in exposed alpine and treeline terrain.

The mid-pack has been reported as being well-settled. Deep persistent layers that may be found around Bear Pass and north appear to have mostly become unreactive at this time.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Avoid the runout zones of avalanche paths. Avalanches could run full path.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.

Problems

Storm Slabs

An icon showing Storm Slabs

Around 50 to 100 cm of snow has accumulated across much of the region, falling with strong southwest wind. The snow and wind has rapidly formed storm and wind slabs that likely resulted in an avalanche cycle on the weekend. With another 20 to 40 cm of snow coming Sunday night into Monday and strong wind, the avalanche cycle may continue.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1.5 - 2.5

Persistent Slabs

An icon showing Persistent Slabs

Around 100 cm of snow may not bond well to weak layers formed in late January and early February, including surface hoar and/or faceted grains. Shallower slabs have the potential of stepping down to these layers, forming very large avalanches.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

2 - 3.5

Valid until: Feb 22nd, 2021 4:00PM