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Avalanche Forecast

Archived

Dec 4th, 2012–Dec 5th, 2012

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

Regions

Kananaskis.

Another day with HIGH danger ratings for the alpine due to extensive redistribution of storm snow and rapid slab formation, primarily on north and east aspects. Pockets of increased danger may exist at treeline as well.

Confidence

Good

Weather Forecast

Strong to extreme W-SW winds are expected to persist for another day and with so much loose dry snow available for wind transport we are seeing rapid loading onto lee aspects and the storm slabs are stiffening and becoming more reactive to loading.  Temperatures over the next 24+ hours will drop into the -20 degree range at 3000m elevation.

Avalanche Summary

One skier controlled Size 2 on NE as at TL.  50-70cm deep x  75m wide.  Ran full path (a 30m high convex roll).  Storm slab was F-4F resistance overlying a 1F old snow surface.  Limited observations due to obscured sky conditions.

Snowpack Summary

Extensive redistribution of storm snow at TL/ALP with cornice growth enhanced.  Test profile at TL produced minor CTM12-15 (SP) in top 20cm of settled HST.  CTH 26 (SP) down 88cm on 121106 RC.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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.