Stormy conditions have elevated the avalanche danger to HIGH. Touchy storm slabs may take some time to settle and bond.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Saturday
Weather Forecast
Strong southerly winds and heavy precipitation overnight with the freezing level at about 1200 metres. Snow ending Saturday morning as the storm moves to the east, winds becoming moderate westerly and temperatures cooling as freezing levels drop to about 600 metres. Light southwest winds on Sunday with broken skies in the afternoon and freezing levels rising rapidly to 2500 metres. Clear skies and light southwest winds on Monday with freezing levels around 3000 metres.
Avalanche Summary
No new avalanches reported. Suspect poor visibility and travel conditions limited alpine observations. Observations from the Whistler area that start zones were easy to trigger, and storm slabs developed rapidly re-loading start zones throughout the day.
Snowpack Summary
Rain on Friday up to about 900 metres and moist snow up to 1600 metres. Strong to extreme southerly winds at 2000 metres and above developing storm slabs with heavy precipitation. Below the new storm slabs there is about 40 cm of recent snow above 60-80 cm of moist snow or a rain crust below 1800 metres. Cornices were already large before the new storm, and new growth is expected to be fragile. Where it still exists, the mid-January surface hoar layer may be found between 100 and 180 cm below the surface. The combination of heavy storm loading and warm temperatures has likely flushed out this weak layer in most areas. However, there is still some uncertainty regarding the sensitivity and distribution of this persistent avalanche problem, especially at high elevations in the north of the region where it remains reactive in snowpack tests (hard to initiate but sudden "pops" results).
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.