Avalanche Forecast

Archived

Mar 23rd, 2016–Mar 24th, 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 unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Kananaskis.

Terrain selection and route finding is key out there. Good situational awareness and discipline are crucial for this week or until the snowpack gets into spring mode. The snowpack is highly complex so do not fool yourself into believing otherwise.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

The Jet stream is to the north of the Rockies at moment. Tonight the winds are forecast to be strong out of the west through the evening. Winds will taper in the am and the freezing levels are set for 1600 meters with trace precipitation in the next 24 hrs.

Avalanche Summary

Yesterday Banff Visitor Safety Forecasting team did avalanche control on the Bourgeau 4 path and got a size 2.5 slab avalanche result. Temperatures were cool this morning but freeze levels have been in the 1800-2000 meter range so activity coincides with the sun and warming air in the afternoon. Pay attention to the daytime heating and any new storm loads over the next while.

Snowpack Summary

We continue to see evidence that our snowpack is not yet a spring snowpack and still very much a winter snowpack. The upper snowpack is complex with 4-5 melt form crusts that vary in depth from just below the surface and up to 80cm deep. These melt form crusts, particularly the Feb11th crust are highly suspicious as we saw many large size 2.5-3.0 avalanches out of steep hanging alpine walls. some initiated by cornice failures and others failing with heat (solar or ambient air temperatures approaching zero degrees). The second and biggest concern for us at the moment is the Jan 6th interface (facets) buried anywhere from 60-110cm in the snowpack - a legitimate deep Persistent Weak Layer. This is the layer that is associated with the very long drought we had that started shortly after Dec 20th and extended into the 2nd week of January before another storm buried these facets. This layer is showing highly variable results in snowpack tests and high degree of variability in its distribution. Essentially we have a very low degree of confidence as forecasters in the snowpack.

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.

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.