Weather Forecast
Unsettled conditions in the wake of Tuesday's storm system are expected to produce cloudy conditions and isolated light flurries with a few centimetres each day for the forecast period. The freezing level is expected to drop to and remain around 800 m, and the winds should remain light and variable.
Avalanche Summary
Reports from Monday are limited to occasional glide avalanche activity to Size 2.5 in the Coquihalla area. Natural avalanches probably occurred on Tuesday in response to heavy loading from snow, wind, and/or rain. Check out the telemarktips.com South Coast conditions forum for a report of a remotely triggered Size 3 slab avalanche on a north facing couloir in the east side of the Duffey Lake area on Sunday. The slab failed on basal facets and propagated 300m out of the couloir and wrapped around to the adjacent northwest.
Snowpack Summary
As of Tuesday morning, 15cm of new snow in the Duffey Lake area adds to the 40-70cm of snow that fell over the past week, while light rain fell in the Coquihalla area. The past week's snowfall overlies a predominately crusty interface, except north facing slopes at treeline and above where small surface hoar (5mm) may be found. Recent reports include hard but sudden compression tests results and a Rutschblock 4 whole block failure on this late-March surface hoar in the Duffey Lake area. In the north of the region, persistent early February layers linger deeper and could fail as large step-down slabs. Cornices are huge and potentially very destructive.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
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.