Avalanche Forecast

Issued: Feb 24th, 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.

Avalanche Canada mconlan, Avalanche Canada

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Northwest Coastal.

Another avalanche cycle may occur on Thursday, as snow and extreme wind are forecast. Travel in avalanche terrain is not recommended.

Summary

Confidence

High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

WEDNESDAY NIGHT: Cloudy with snowfall, accumulation 15 to 25 cm, 100 km/h southwest wind, alpine temperature -6 C, freezing level rising to 500 m.

THURSDAY: Cloudy with snowfall, accumulation 10 to 20 cm, 80 km/h northwest wind, alpine temperature -5 C, freezing level 700 m.

FRIDAY: Cloudy with snowfall, accumulation 15 to 25 cm, 40 to 60 km/h northwest wind, alpine temperature -7 C.

SATURDAY: Cloudy with snowfall, accumulation 5 to 10 cm, 40 to 60 km/h southwest wind, alpine temperature -5 C.

Avalanche Summary

More evidence of the avalanche cycle from earlier this week was observed as the skies cleared. For example, check out this MIN near Shames. This MIN shows excellent photos of slab avalanches around treeline elevations, potentially releasing on the surface hoar described in the Snowpack Summary.

Looking towards Thursday, another natural avalanche cycle may be triggered as a substantial amount of new snow and extreme wind are forecast. It will be a good day to stay well away from avalanche terrain!

Snowpack Summary

The region may see anywhere from 20 to 40 cm by Thursday afternoon above 800 m, with associated strong to extreme southwest to northwest wind. Storm slabs are expected to build rapidly in sheltered terrain and wind slabs in exposed terrain at high elevations. Below 800 m, rain will soak a snowpack that was recently wet. 

This snow will add to the 100 cm of snow that fell on the weekend, which may not be bonding well to previous surfaces buried mid-February, including:

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

The mid-pack has been reported as being well-settled. There are presently no deeper concerns.

Terrain and Travel

  • Travel in alpine terrain is not recommended.
  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • 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

20 to 40 cm o snow is expected to accumulate by Thursday afternoon, forming new storm slabs. The wind is forecast to howl from the southwest to northwest, so wind slabs will rapidly build at treeline and alpine elevations too. Including the weekend's snow, around 80 to 120 cm of recent storm snow will have built above the surfaces formed mid-February, potentially including weak surface hoar and/or faceted grains. All of this stacks up to another natural avalanche cycle expected for Thursday.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1.5 - 2.5

Valid until: Feb 25th, 2021 4:00PM

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