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 rising to 2100 metres with alpine high temperatures around -1 to 0. Weak overnight cooling.Friday: Cloudy with light flurries beginning in the afternoon and continuing overnight. Light to moderate southwest winds. Freezing level to 2200 metres with alpine high temperatures around 0 to +1.Saturday: Cloudy with continuing flurries bringing 10-15 cm of new snow. Moderate to strong southwest winds. Freezing level to 1800 metres with alpine high temperatures around -3.
Avalanche Summary
Observations from Tuesday showed numerous small (size 1) storm slabs releasing both remotely and with ski cutting. Crown fractures were in the 35-40 cm range and activity was observed at all elevations and on all but west aspects.Poor visibility hindered observations of avalanche activity on Monday.On Sunday, warming and sunny breaks initiated widespread natural storm slab and loose, wet avalanche activity in the recent storm snow, up to size 2, on all aspects from 1500-2300 m.In addition to heightened storm slab activity following regular snowfalls, observations from late last week also showed a pattern of heightened cornice failure activity. Reports of 'bus sized' blocks found in debris as well as a suspected cornice-triggered size 4 wind slab release in the adjacent North Columbias and Glacier National Park should keep these looming giants top of mind.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
About 70-100 cm of recent storm snow overlies a crust on all aspects to at least 2300 m (and possibly higher on south-facing slopes). Recent variable strong winds have pressed and redistributed the most recent accumulations into new wind slabs on a range of aspects.Within the upper snowpack there are now a few different crusts with the shallowest of these (down 30-50 cm) remaining 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 80 to 120 cm below the surface. This buried crust/surface hoar interface was widely reactive but has not produced any avalanche activity in the past week. It 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 larger triggers such as; sleds, step-down from a surface avalanche or, a 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.