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Avalanche Forecast

Archived

Mar 14th, 2016–Mar 15th, 2016

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

Regions

Kananaskis.

A healthy dump of snow and a medium avalanche cycle recently, its imperative to give the new snow time to settle out. This is prime time for skier triggered slab avalanches with potential also for stepping down to deeper layers. Cornices are immense.

Confidence

Moderate - Due to the number and quality of field observations

Weather Forecast

Cloudy with sunny periods and some convective flurry activity for Tuesday.  Alpine temperatures at -8.0 and winds will be westerly light to moderate at upper treeline and moderate northwesterly winds in the alpine.  Freezing levels will be valley bottom. 

Avalanche Summary

A notable avalanche just outside the ski area boundary at Sunshine Village Ski area.  A skier triggered a size 2.5  which was initiated on a crust which was buried February 11th and then proceeded to step down to basal facets causing the slide to dig to the ground and take the entire depth of the snowpack along with it.  He took a ride for about a 100 meters and luckily pulled out of it.  Yesterday there was report of a size 2.5 -3.0 off of Mt. Robertson that went ran to valley bottom and likely could have took out the normal path that ski tourers would take if exiting down the Robertson glacier and out the valley for the French/Haig/Robertson traverse.

Snowpack Summary

Up on the Spray today, light convective flurries continued with intermittent windows of good visibility.  The recent storm (30-35 cm) snow has had some wind affect in specific treeline and alpine features that are exposed to the winds. So expect to see this in cross wind affected and in the immediate lee of the wind.  Anticipate a bit of reverse loading as the upper flow is from the northwest so keep a sharp eye out for recent wind slabs on south through easterly aspects in the alpine.  Within the mid depths of the snowpack are crusts buried from early March and February that we have seen little activity on but remain fantastic bed surfaces for avalanches especially in the presence of wind slabs.  In the alpine, I am probing constantly to make sure I'm not walking into shallow, rocky snowpack areas where the potential for triggering deeply buried facets from early January is still possible.  The big thing to keep in mind over the next few day is there is great deal of storm snow available for the wind to have its way with it and build some nasty wind slabs that could spoil your day.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.