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Avalanche Forecast

Archived

Mar 6th, 2020–Mar 7th, 2020

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

Regions

South Rockies.

Avalanche danger will increase rapidly as heavy snowfall blankets the region through Saturday - with the greatest accumulations expected along the BC/Alberta border. Back off to simple terrain that is free of overhead hazards as depths increase - and enjoy the new snow!

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Friday night: Cloudy with increasing flurries bringing 5-10 cm of new snow. Moderate southwest winds.

Saturday: Cloudy with continuing snowfall bringing 15-25 cm of new snow. Light south winds, becoming moderate or strong at ridgetop. Alpine high temperatures around -7.

Sunday: Mainly cloudy. Light to moderate southwest winds. Alpine high temperatures around -9.

Monday: Mainly sunny. Light to moderate southwest winds. Alpine high temperatures around -8.

Avalanche Summary

No avalanches have been reported since last week, but there have been limited field observations. A few natural size 2 wind slabs have been reported on north and east aspects in the neighbouring Kananaskis region.

A very large (size 3) deep persistent slab avalanche was observed north of Sparwood last Friday on a steep southeast facing alpine slope. This follows a pattern of sporadic deep slab releases in the upper Elk Valley including this natural avalanche from Feb 11 and this sled triggered avalanche from Feb 9. These types of large avalanches will be most likely during periods of heavy loading or intense warming.

Snowpack Summary

20-30 cm of new snow is expected to accumulate in the region by the end of the day on Saturday, targeting the east slope of the region in particular. The new snow will bury recent wind slabs and wind effect in exposed terrain as well as sun crust on solar aspects and temperature crust up to 1700 m on all other aspects. The new snow is not expected to bond well with any of these surfaces over the near term.

A thick rain crust currently sits 40-80 cm below the surface and can be found up to 2100 m. Avalanche activity was last observed at the faceting interface between this crust and overlying snow on February 17. The mid-pack is well settled and strong, but the base of the snowpack contains basal facets that are most prominent in shallow rocky start zones.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
  • Avalanche hazard is expected to to increase througout the day, think carefully about your egress.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.