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Avalanche Forecast

Archived

Feb 24th, 2021–Feb 25th, 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 possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

North Columbia.

Watch for fresh and reactive storm slabs forming Thursday as new snow arrives amid strong wind. Keep in mind the potential for triggering deeper slabs may persist even as natural activity from the previous storm tapers off.

Confidence

High -

Weather Forecast

Local enhancements in snowfall amounts possible in the Monashees and near Blue River.

WEDNESDAY NIGHT: Increasing cloud with flurries bringing up to 5 cm in most areas, strong southwest wind, freezing level valley bottom.

THURSDAY: 5-10 cm new snow in most areas, strong southwest ridgetop wind easing to moderate, freezing level 1100 m.

FRIDAY: 5-15 cm of new snow, light to moderate westerly wind, freezing level 800 m.

SATURDAY: A trace of new snow, light to moderate southwest wind, freezing level 800 m.

Avalanche Summary

The Selkirks (eastern ranges of the region) were the hotspot for storm activity over the weekend and into Monday, with widespread natural wind and storm slab avalanches size 2-3 and explosive triggered size 3-4, many running to valley bottom.

Reports from the Monashees indicate a natural cycle to size 2.5 storm slabs peaking over the weekend and becoming more stubborn to human triggers as the storm tapered. Explosive work on Tuesday in the northern Monashees produced limited results including a few size 1's and and one size 2 cornice triggered storm slab.

We've had no reports of storm avalanche activity stepping down to deeper persistent layers.

Snowpack Summary

10-15 cm of new snow is forecast to fall by the end of the day Thursday. It falls over 40-80 cm of recent storm snow which is well settled at lower elevations and heavily wind affected at upper elevations. Wind deposits up to 100 cm deep can be found in lee terrain features in the alpine and may remain reactive to human and machine triggers. 

All of this recent snow sits over facetted surfaces from the cold snap. There is uncertainty around how long it will take for this interface to bond but reports from the Monashees have indicated a positive trend already.

We've now got 70 to 120 cm of snow above the late January persistent weak layer which is composed of surface hoar in openings in the trees and/ or a crust on steep solar aspects. An absence of step-downs to this layer in the most recent storm cycle indicate that is has likely healed.

Terrain and Travel

  • Be carefull around freshly wind loaded features.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.

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.