Variable snowpack conditions, particularly at upper treeline and alpine elevations. The snowpack is proving slow to recover following the recent big storm.
Confidence
Fair - Due to variable snowpack conditions
Weather Forecast
Synopsis: Northwest flow will bring occasional flurries and cooler temps until Tuesday, when a low pressure system is expected to impact the region.Sunday and Monday: Occasional flurries. Sunny breaks in the cloud giving daytime warming both days. Afternoon freezing level around 700 m. Winds mostly light nothwesterly, but occasionally gusty.Tuesday: Moderate, maybe heavy snowfall starting in the afternoon. Models currently disagree with track and intensity of this system. Freezing level going to around 1500 m. Southwest winds to 60 km/h at ridgetop.
Avalanche Summary
On Friday, a size 2.5 natural loose wet avalanche was reported from the Coquihalla. Along the Duffey, small skier-triggered avalanches could be triggered on north aspect slopes at treeline, with crowns of 30 cm in the recent storm snow.
Snowpack Summary
The recent storm delivered around 60 cm of heavy snow at upper elevations and a mix of rain and snow below around 1900 m. Below 1500m, the snowpack was reported to be isothermal as of Friday afternoon. On Friday night, 5-15 cm new snow fell. This insulating layer will further delay the re-freezing process, despite cooler temperatures. Below the recent storm snow lies one or two weak layers buried approximately 50 cm below the surface. These comprise faceted snow, surface hoar and/or a crust. As a result of all these factors, the snowpack structure is highly 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. The mid-pack is strong and well settled, although the entire snowpack will remain volatile below 1500m until it has a chance to freeze.
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.