Surface instabilities and cornice hazards should be firmly on your radar as you travel. Expect stability to deteriorate over the course of each day.This is our final regular forecast of the season and will expire on April 25.
Weather Forecast
Tuesday: Mainly sunny. Light south winds, increasing to strong at ridgetop. Freezing level to 3000 metres with alpine high temperatures around +4. Weak overnight cooling.Wednesday: Sunny. Light west winds. Freezing level rising to 3500 metres by late afternoon and staying steady overnight. Alpine high temperatures around +6.Thursday: Sunny. Light south winds. Freezing level to 3300 metres with alpine high temperatures around +8.
Avalanche Summary
Several smaller (size 1.5) natural wind slab avalanches were observed in the region on Saturday. These occurred primarily on northwest aspects above 2400 metres.Reports from Thursday were limited to a couple of size 2 storm and wind slabs, 30 and 50 cm deep, respectively. The storm slab released naturally while the wind slab was ski cut from a steeper north aspect in the alpine.Tuesday's reports included observations of numerous natural wind slab release from size 1-2 on north through east aspects in the alpine. A skier triggered size 2 storm slab resulted in a near miss. Another recent very large (size 3.5) storm slab was also observed to have released on a large, wind-loaded alpine feature. Observations from just over a week ago also showed a pattern of heightened cornice failure activity. Looking forward, a period of increasing warming, full sun, and warm overnight temperatures will be maintaining elevated chances of cornice and loose wet avalanche activity.
Snowpack Summary
A surface crust is likely to exist on all but north aspects in the alpine and is expected to undergo melt-freeze cycles with daily warming and overnight cooling. Below the surface, about 50-70 cm of settled storm snow from the past couple of weeks overlies a supportive crust that exists on all but north aspects above about 2200 metres.This layer as well as the deeper (down about 90-120 cm) mid-March crust are of limited concern concern after warm temperatures have promoted settlement and bonding in the upper snowpack. Any remaining uncertainty with regard to their strength is generally limited to high north aspects as well as the possibility for triggering with a heavier load, such as a cornice collapse.Deeper persistent weak layers from December and January are generally considered dormant at this time but may be reactive to very large triggers. Cornice collapses become increasingly likely during periods of intense daytime warming.
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.