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Avalanche Forecast

Archived

Mar 7th, 2012–Mar 9th, 2012

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 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.

Regions

South Rockies.

Confidence

Fair - Intensity of incoming weather is uncertain on Friday

Weather Forecast

Thursday: A ridge of high pressure will bring dry and bright conditions with generally light northwesterly winds and freezing levels rising to around 2000m. Friday: A Pacific frontal system will bring around 5 mm precipitation, which may fall as a mix of snow and rain. Freezing levels will be up to 2000m. Winds will be strong southwesterly. Saturday: Another frontal system moves through late in the day, bringing further light to moderate amounts of precipitation, cooler temperatures and strong winds.

Avalanche Summary

On Wednesday, a size 2 avalanches was reported from around 2300 m in the South York Creek area on an east aspect. Limited amounts of sluffing from solar activity was also noted. On Tuesday there was a report of a snowmobile-triggered avalanche, details are limited at this time. On Tuesday, professionals were successfully & intentionally triggering small avalanches during control work in the new snow.

Snowpack Summary

20 to 50 cm of recent storm snow reported from the regions. Feb. 09 surface hoar is now down between 40 & 100cm. The depth varies throughout the region. This weak layer continue to perform and snowpack tests continue to show sudden moderate failures on this interface. The weekend's strong winds and mild temperatures formed the upper snowpack into a more cohesive slab. Lingering concern remains for basal facets, particularly in shallower snowpack areas with steep, rocky start zones. I suspect windslabs are developing with the forecast wind and recent snow.

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.

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.

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.