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Avalanche Forecast

Archived

Feb 26th, 2021–Feb 27th, 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.

Storm slabs may continue to be reactive, especially in wind loaded terrain, and on south facing slopes if solar radiation is strong.

There is the potential to trigger deeper weak layers, resulting in large avalanches. Choose conservative terrain.

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.

Weather Forecast

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

SATURDAY - A mix of sun and cloud with isolated flurries / moderate northwest wind / alpine high temperature near -13

SUNDAY - Mainly cloudy with a few flurries, 5 cm / strong southwest 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

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 recent days. 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 recent 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

  • Use conservative route selection and resist venturing out into complex terrain.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be carefull around freshly wind loaded features.
  • Even brief periods of direct sun could produce natural avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.