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Avalanche Forecast

Archived

Feb 26th, 2021–Feb 27th, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells.

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. 

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

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.