Confidence
Fair - Due to variable snowpack conditions
Weather Forecast
Synopsis: Northwest flow gives way to a frontal system that impacts the region on Tuesday afternoon and into Wednesday.Monday: Patchy convective snowfall. Some areas may see nothing, others 2-5 cm. Some sunny breaks in the cloud giving daytime warming. Afternoon freezing level around 800 m. Winds gusty from the northwest.Tuesday: Day starting clear, but clouding over then moderate snowfall starting in the afternoon. 10-20 cm overnight. Freezing level around 1200 m. Southwest winds increasing to 60 km/h at ridgetop.Wednesday: Around 20 cm new snow. Freezing level around 1200 m. Southwest winds around 25 km/h.
Avalanche Summary
On Saturday, a size 1.5 natural avalanche was reported from a north aspect at 1900 m, with a crown of 50 cm failing on the surface hoar/crust layer from March 11th. Soft slab avalanches to size 1.5 could also be triggered on this layer from steep rolls at treeline and below treeline. On Friday, loose natural avalanches up to size 2.5 were reported from treeline and below treeline due to warm daytime temperatures. Two skier-triggered avalanches and one vehicle remote triggered avalanche were also reported from north aspect slopes between 1800 and 2000 m.
Snowpack Summary
10-20 cm new snow now sits on a weak crust below 1900 m. Below the crust is moist snow, from the previous intense, wet storm. Freeze-up following this storm was slow, due to a slow decline in temperatures and the insulating skiff of snow on the surface. Below the recent new snow lies one or two weak layers buried approximately 60 cm below the surface. These comprise faceted snow, surface hoar and/or a crust. The snowpack structure is quite variable at this time. It may change dramatically with only a subtle change in elevation, aspect, wind or sun exposure. With further cooling, the upper snowpack should start to bond better. However, with the amount of moisture and the insulating effect of the new snow, expect this to take longer than usual. Mid and lower snowpack layers are well bonded.
Problems
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.
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.