Avalanche Forecast

Archived

Mar 7th, 2013–Mar 8th, 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 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

South Rockies.

Confidence

Fair - Timing or intensity of solar radiation is uncertain for the entire period

Weather Forecast

A weak upper trough over the South Rockies is slowly dissipating providing more clearing and less precipitation with only trace amounts of snow forecast for Friday. Overnight into Friday: Trace accumulations only. Freezing levels remain close to valley bottom even during the day and winds will be light.Saturday: No new precipitation. Good freeze overnight, but daytime temperatures could rise to over 1500m with clear skies. Winds light from the North West.Sunday: More of a western zonal weather pattern expected. Light precipitation possible. Warmer daytime temperatures with freezing levels up to 1800m. Winds light from the South West.

Avalanche Summary

Numerous natural loose dry avalanches up to size 1.5 were observed throughout the forecast region on Thursday. They mostly occurred in steep terrain and entrained recent storm snow.Ski cutting and cornice cutting tests in the Harvey Pass area produced loose and soft slab avalanches to size 1.5.

Snowpack Summary

Approximately 20 cm of new low density snow has fallen in the last 24hrs which brings the total snow recent storm totals to 70 cm. 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. South west winds have contributed to cornice growth and soft slabs formation in open areas in the alpine and treeline. All of the recent snow accumulations overlie a rain crust which exists up to about 2000m in elevation in much of the forecast area. Mid and lower pack is 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 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.

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.