Avalanche Forecast

Issued: Mar 5th, 2021 4:00PM

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

Avalanche Canada astclair, Avalanche Canada

Triggering large storm slab avalanches at upper elevations remains likely in the north of the region, especially in wind-drifted areas. Continue to make conservative terrain choices while the storm snow settles and stabilizes.

Summary

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Friday night: Overcast, up to 5 cm of snow in the north of the region, moderate southwest winds, freezing level dropping to 700 m. 

Saturday: Mostly cloudy, isolated flurries with trace accumulations, light southwest winds, freezing level near 1300 m.

Sunday: Mostly cloudy, isolated flurries with trace accumulations, light southwest winds, freezing level near 1200 m and dropping to valley bottom.

Monday: Partly cloudy, light southeast winds, freezing level near 1200 m.

Avalanche Summary

In the north of the region, a small skier-triggered wind slab was reported on Thursday.

There are still concerns about the reactivity of persistent weak layers in these areas. Over the past week, observers near Duffey Lake reported a large (size 2.5) avalanche on a north aspect at 1750 m that was thought to have released 1 m deep on a persistent weak layer. On Sunday, a size 1.5 skier accidental was reported on a northwest aspect in the alpine, also near Duffey Lake. The slab is thought to have failed on a thin layer of facets, sandwiched between two wind-stiffened layers. 

In the south of the region, there have been numerous reports of large (size 2-2.5) natural glide slab avalanches. Glide slabs are most likely in areas of smooth ground cover such as rock slabs at lower elevations experiencing prolonged warm temperatures with limited overnight refreeze. These avalanches will be large, involving the full depth of the snowpack. Carefully consider your access/egress routes where they cross under large paths. 

Snowpack Summary

In the north of the region, 20-30 cm of snow accumulated Friday, with higher totals near the Hurley. This snow was accompanied by strong south winds, forming touchier slabs on leeward slopes. Massive cornices exist on ridgelines, which can act as triggers on slopes below. 

The load from new snow and wind has the potential to wake up buried weak layers. A layer of facets from mid-February has shown reactivity on north aspects near treeline and is primarily a concern where it separates wind-stiffened snow above and below. A deeper persistent weak layer buried in late January composed of a crust, facets or surface hoar also has the potential to re-awaken with large triggers, such as an avalanche in motion, cornice fall, or intense loading from snow/ wind. The lower snowpack is well settled and strong in most areas.

In the south of the region, danger ratings are Moderate, Low, Low due to a gradual cooling trend in the aftermath of a significant warm-up. The snowpack is generally well consolidated with no concerns of buried weak layers but notable glide avalanche activity.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Cornice failure may trigger large avalanches.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Problems

Storm Slabs

An icon showing Storm Slabs

In the north of the region, 20-30 cm of snow rapidly accumulated above 1400 m on Friday, forming a widespread reactive storm slab problem. Storm slabs may be more reactive in wind-drifted areas. The combination of wind and snow has the potential to weaken cornices, which can act as triggers on slopes below.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1.5 - 3

Persistent Slabs

An icon showing Persistent Slabs

In the north of the region, a weak layer of facets buried in mid-February is a lingering concern, primarily in areas where it separates wind-stiffened snow above and below. This snowpack structure is most suspect on northerly aspects at upper treeline elevations. Large triggers, such as an avalanche in motion, cornice fall, or intense loading from snow and wind could initiate this deeper layer. 

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Mar 6th, 2021 4:00PM