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Avalanche Forecast

Archived

Feb 25th, 2021–Feb 26th, 2021

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

Regions

South Columbia.

New snow and wind will mean that storm slabs are to be expected, and will likely be reactive to human triggering in many areas.

The potential exists to trigger deeper weak layers, resulting in large avalanches. Choose conservative terrain.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

THURSDAY NIGHT - Flurries, 10-15 cm / moderate to strong west wind / alpine low temperature near -10 

FRIDAY - Mainy cloudy with flurries, 5 cm / moderate northwest wind / alpine high temperature near -10

SATURDAY - A mix of sun and cloud with a few flurries / moderate west wind / alpine high temperature near -12

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

Avalanche Summary

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, reported in the Selkirks in the northern part of the region.

The Monashees had surprisingly limited activity up to size 2 in the same time period. Reports from Monday described size 1-2 natural, explosive, and human-triggered avalanches, as well as one report of a size 3 natural cornice triggered avalanche.

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

10-15 cm of new snow is expected on Thursday night with another 5 cm on Friday. This will add to the 60-100 cm of recent storm snow. 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, usually skier triggered in steep, cliffy, unsupported terrain around treeline in the south of the region.

Terrain and Travel

  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Be carefull around freshly wind loaded features.

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.