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Avalanche Forecast

Archived

Dec 12th, 2022–Dec 13th, 2022

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

Regions

North Columbia, South Columbia, Esplanade, Jordan, North Selkirk, West Purcell, Badshot-Battle, Central Selkirk, Goat, Gold, Whatshan.

Numerous persistent slab avalanches caught both professionals and recreationalist off guard over the last few days. Use extra caution at treeline where triggering a persistent slab is more likely.

Read our featured blog on understanding how to manage a persistent slab problem when traveling in the backcountry.

Confidence

Moderate

Avalanche Summary

On Monday, a pair of size 2 human-triggered avalanches were reported in the RMR backcountry. These included a skier accidental and a skier remote from 50 m away on the mid-November layer. This is just the latest in a number of persistent slab avalanche reports from the last few days.

Throughout the weekend numerous size 2 storm slab avalanches were observed on the Dec 5 surface hoar weak layer. Whumpfing and cracking were observed throughout the region.

Snowpack Summary

Moderate southwest ridgetop winds have redistributed 40 - 50 cm of storm snow into deep pockets at higher elevations. On south facing slopes this new snow has fallen on a sun crust and in sheltered terrain it sits over a layer of surface hoar.

Buried 60 to 90cm deep, a persistent layer of surface hoar, crust, and faceted crystals is the primary concern within the snowpack. This layer has been most reactive at treeline between 1700-2200 m, but it was also observed as low as 1450 m and on all aspects.

Snowpack depths are highly variable and range from 90cm at treeline to 200cm in the alpine in wind-affected locations.

Weather Summary

Monday Night

Mainly clear skies with northerly ridge winds 25 km/hr. Alpine temperatures, low of -10. Freezing levels valley bottom.

Tuesday

Mainly clear in the morning. Scattered cloud in the afternoon with the possibility of isolated flurries in the evening, trace accumulation. Northerly ridge wind 25 - 40 km/hr. Alpine temperatures, high of -6. Freezing levels valley bottom.

Wednesday

A mix of sun and cloud. Northwesterly ridge winds 30 - 50 km/hr. Alpine temperatures, high of -7. Freezing levels valley bottom.

Thursday

Clear skies. Northwesterly ridge winds 20 - 40 km/hr. Alpine temperatures, high of -8. Freezing levels valley bottom.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Give the new snow time to settle and stabilize before pushing into bigger terrain.
  • Avoid open slopes and convex rolls below treeline where weak layers may be preserved.
  • Be aware of the potential for large, destructive avalanches due to the presence of deeply buried weak layers.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.

Problems

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.

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.