Progressive warming and no overnight freeze is forecasted for the week of May 3 through to May 5th. Widespread avalanche cycle is expected. Check Alberta511 for up to date road closures on Maligne road and Hwy 93 for Wednesday through Friday.
Weather Forecast
Rapid progressive warming expected by Wednesday evening and leading into the weekend. Mix of light precipitation and broken skies. Expect strong radiation with any direct sun. Freezing level rising to 3000m by midnight on Wednesday.
Snowpack Summary
Winter conditions exist in the high alpine on Northerly slopes with up to 20 cm of loose new snow sitting over a well consolidated upper snowpack. Spring conditions exist on all other aspects and elevations with a melt freeze crust that is dependent on overnight freezing conditions. The snowpack is moist to wet snow to ground below this crust..
Avalanche Summary
Avalanche activity will increase after warm nights and/or with thermal inputs such as rain, solar radiation and daytime warming. The avalanche danger will be lowest after cold nights and strong crust formation and will increase into the afternoon and evening before sunset. Likely trigger spots are rocks, cliffy terrain and shallow snowpack areas.
Problems
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.
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.