Avalanche Forecast

Archived

Mar 8th, 2013–Mar 9th, 2013

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

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

South Rockies.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Saturday

Weather Forecast

The ridge of high pressure moves south eastward over the South Rockies bringing mostly clear skies for Saturday. The timing of the next wave of moisture from the return of a more westerly zonal flow is uncertain. Current models suggest Monday mid day. Overnight into Saturday: Mostly clear skies with the possibility of some morning fog patches. Light winds out of the north west at ridge top are expected and freezing levels could rise to 1800 m with the influence of some warmer air. Sunday: Cloudy with sunny breaks, chance of light precipitation. Alpine temperatures near -7.0. Winds increasing, moderate to strong from the west.Monday: Timing of the next system is uncertain, but some models are showing light to moderate snowfall amounts for the region by later Monday.

Avalanche Summary

A natural cycle of loose and soft slab avalanches up to size 1.5 occurred Thursday and into Friday throughout the forecast region. An out of bounds skier near Castle Mtn triggered a size 2 slab avalanche in steep north east facing terrain on Gravenstafel Ridge on Thursday.

Snowpack Summary

Approximately 30 cm of low density snow has fallen in the last 48hrs. Greatest accumulations have occurred in the Elk Valley South and Flathead regions, while areas such as Elk Valley North and Crowsnest pass may not have seen as much new snow. Southwest winds have contributed to cornice growth and soft slab formation in open areas in the alpine and treeline. The recent snow accumulations add to the variable amounts of settled storm snow that overlies a widespread melt freeze crust. This supportive crust exists up to about 2000m in elevation in much of the forecast area. The mid and lower pack are strong and well settled.

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 Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.