Forecast sunshine and warming will increase the likelihood of triggering in a wide range of avalanche problems on Thursday. Expect stability to deteriorate over the day.
Weather Forecast
Thursday: Mainly sunny. Light southeast winds shifting southwest. Freezing level to 2200 metres with alpine high temperatures around 0. Weak overnight cooling.Friday: Mainly cloudy with light flurries beginning in the afternoon and increasing overnight. Light southwest winds. Freezing level to 2300 metres with alpine high temperatures around 0 to +1.Saturday: Cloudy with continuing flurries bringing 5-10 cm of new snow. Moderate to strong southwest winds shifting to west. Freezing level to 1800 metres with alpine high temperatures around -3.
Avalanche Summary
An early observation from Wednesday detailed a natural size 3 slab avalanche that is believed to have released over a persistent weak layer, potentially from mid-March. Evidence of the release was seen from a distance in the Dogtooth range.Reports from Tuesday included several observations of large (size 2) natural storm slab releases focused around steep features just below ridgetop.Poor visibility limited observations of avalanche activity on Monday.On Sunday there was a report of a near miss for skiers who triggered a size 2 wind slab on a north aspect at treeline in the northern part of the region. The northwestern part of the region saw a warming-induced natural avalanche cycle up to size 3 on large alpine features in the recent storm snow.Looking forward, a trend toward clearing skies and warming temperatures will be increasing chances of loose wet avalanche activity as well as testing the strength of storm slabs and wind slabs formed in the wake of recent snowfall and wind events.
Snowpack Summary
Generally 30-40 cm on recent storm snow overlies a crust on all aspects to at least 2000 m (and possibly higher on south-facing slopes), with up to 80 cm observed in some areas in the northwest of the region. Recent shifting strong winds pressed and redistributed the most recent accumulations into new wind slabs on a range of aspects. Below 2200 m the new snow has a thin surface crust that breaks down to moist or wet snow in the afternoons.Within the upper snowpack there are now several buried crusts with the mostly recently buried (down about 20 cm) posing a concern as the uppermost layer of storm snow settles and bonds to it.There is some lingering concern around the mid-March persistent weak layer in the alpine where it is found 60 to 100 cm below the surface. This buried crust/surface hoar interface is likely trending towards dormancy, but we need to keep it in the back of our minds as it is capable of producing large avalanches should it be triggered (think step-down from a surface avalanche or cornice collapse)Deeper persistent weak layers from December and January are considered dormant at this time.
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.
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.