Avalanche Forecast

Issued: Feb 26th, 2021 4:00PM

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

Avalanche Canada kdevine, Avalanche Canada

Wind slabs continue to be a concern on all aspects due to recent variable wind directions. Be wary of south-facing slopes when the sun comes out, it could trigger natural avalanches.

Uncertainty surrounding deeper weak layers is best managed with conservative terrain choices. 

Summary

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

FRIDAY NIGHT - Cloudy with clear periods and isolated flurries / light to moderate northwest wind / alpine low temperature near -13 

SATURDAY - Mainly sunny / moderate northwest wind / alpine high temperature near -13

SUNDAY - A mix of sun and cloud / strong west wind / alpine high temperature near -7 / freezing level 1500 m

MONDAY - Mainly cloudy with a few flurries, 5 cm / strong southwest wind / alpine high temperature near -6 / freezing level 1500 m

Avalanche Summary

At the time of publishing on Friday, there were several reports of solar-triggered natural avalanches up to size 2.

There were a few size 1 human-triggered wind slab avalanches reported on Thursday.

On Wednesday, there were a few reports of natural and explosives-triggered size 2 storm and wind slab avalanches, as well as a few natural and explosives-triggered cornices up to size 3. 

There were also a few notable remotely triggered avalanches reported in the north of the region that likely failed on the recently buried facet layer. The MIN report can be viewed here.

On Monday and Tuesday in the north of the region, there were reports of numerous size 1-2.5 natural, human and explosives-triggered storm slab avalanches. 

Further south in the region on Monday and Tuesday, there were reports of natural, explosives and human-triggered size 1-1.5 wind slab avalanches. One notable natural size 2 wind slab on a northeast aspect is suspected to have stepped down to deeper persistent layers.

Earlier in February, there were a few reports of large, sporadic avalanches (size 2.5-3) on southeast aspects in the alpine, likely releasing on a layer of facets on a crust (see a photo here), and a large human-triggered avalanche (size 2.5) on surface hoar near Quartz Creek.

Snowpack Summary

The Purcells have received anywhere from 10-50 cm of fresh snow in the past week. The higher amounts have generally been in the western and northern parts of the region, with lesser amounts to the east and south. This new snow sits on a persistent weak layer of facets that formed during the last cold snap. Recent variable winds have formed wind slabs on many aspects. 

 Another persistent weak layer that formed in late January is now 30-90 cm deep. In the northern Purcells, this layer has been reported as a surface hoar layer at treeline and below, but a combination of facets or crusts could exist at all elevations.

The northern Purcells also have an older surface hoar layer that can still be found 60-120 cm deep at treeline. Additional weak layers may exist near the base of the snowpack. Steep, rocky areas with a shallow, or thin to thick snowpack should be considered possible trigger points.

Terrain and Travel

  • Be especially cautious as you transition into wind affected terrain.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Brief periods of sun could quickly initiate natural avalanche activity.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Choose slopes that are well supported and have limited consequence.

Problems

Wind Slabs

An icon showing Wind Slabs

Wind slabs may continue to be reactive and may exist in many areas due to recent variable wind directions.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

There may be a lingering possibility of triggering persistent slab avalanches in isolated steep terrain features. The primary layer of concern is layer of surface hoar, facets, and/or crusts buried 40-80 cm deep throughout the region. 

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 3.5

Valid until: Feb 27th, 2021 4:00PM