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Avalanche Forecast

Archived

Feb 27th, 2021–Feb 28th, 2021

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

Regions

South Columbia.

Watch for changing conditions as strong winds may mean that wind slabs become increasingly reactive throughout the day. Avoid overhead hazard during times of rapid loading due to strong winds.

There is the potential to trigger deeper weak layers. Choose conservative terrain.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

SATURDAY NIGHT - Cloudy with flurries, 5 cm / moderate southwest wind / alpine low temperature near -12 

SUNDAY - Mainly cloudy with scattered flurries, 5 cm / strong west wind / alpine high temperature near -5 / freezing level 1500 m

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

TUESDAY - Mainly cloudy with isolated flurries / moderate southwest wind / alpine high temperature near -7 / freezing level 1300 m

Avalanche Summary

On Friday, there were numerous reports of size 1-2 natural and human-triggered storm slab avalanches on all aspects, at all elevations.

On Thursday, there were numerous reports of size 1-2 natural, human and explosives-triggered storm slab avalanches. Many of these were triggered remotely (from a distance). 

On Wednesday, there were a few reports of size 1.5-2 natural and human-triggered storm slab avalanches in the alpine and at treeline, on all aspects.

On Tuesday, there were several reports of natural, human and explosives-triggered avalanches up to size 3, though most were in the size 1-2 range.

During the storm last weekend and into Monday, there was a widespread natural and explosives-triggered avalanche cycle, with avalanches ranging from size 2-4. The largest avalanches were reported in the Selkirks in the northern portion of the region.

There have been a few reports from the south of the region of sporadic persistent slab avalanches failing on the late January persistent weak layer. These have been around size 2, human-triggered, and out of steep, cliffy, unsupported terrain around treeline. 

Snowpack Summary

The region has received 60-100 cm of fresh snow in the past week. Deep wind deposits may be found in lee terrain features in the alpine and open treeline areas, and will likely remain reactive to human triggers. All of this new snow sits over weak, faceted snow from the early to mid-February cold snap. 

There is now 70-120 cm of snow above the late January persistent weak layer which is composed of surface hoar in sheltered areas in the trees and/ or a crust on steep solar aspects. Very isolated activity on this layer has been observed recently.

Terrain and Travel

  • Be carefull around freshly wind loaded features.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

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.