Regions
South Coast Inland.
Up to 40 cm of fresh snow in the south of the region is hiding wind slabs that may still be sensitive to human triggering. Overcast skies and isolated flurries are expected to limit the effects of the strong late-winter sun on Sunday.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Sunday
Weather Forecast
The forecast has changed since yesterday. Sunday looks to be cloudy with a chance of flurries for the South Coast Inland. Monday also looks cloudy, but clouds may give way to clear skies on Tuesday. SUNDAY: Overcast, freezing level rising to around 500 m, moderate west/southwest wind, 1 to 5 cm of snow possible.MONDAY: Scattered cloud cover in the morning, increasing cloud throughout the day, freezing level rising to around 800 m, light to moderate west/southwest wind, no snow expected.TUESDAY: Clear skies, freezing level rising to around 1200 m, light variable wind, no snow expected.
Avalanche Summary
Wind slabs were sensitive to skier triggering to size 2 on Friday on north and northeast facing slopes around 2000 m. These slabs were 10 to 25 m wide with crowns averaging 40 cm in depth. On Thursday wind loaded features produced natural avalanches to size 2.5. Several natural wind slab avalanches to size 2 were observed on steep north facing alpine terrain. Control work produced avalanches to size 2 in steep unsupported terrain.On Wednesday a natural size 1 wind slab was reported from an east facing feature at 1950 m. Isolated soft wind slabs were also being observed on steep convexities.
Snowpack Summary
The Coquihalla picked up a surprise 35 to 45 cm of snow Friday and Friday night with light easterly winds which is now hiding previously formed wind slabs. Mainly southerly winds formed these wind slabs as they interacted with up to 120 cm of storm snow that has fallen in the last week. All of the new snow rests on the February 23 weak layer. The February 23 weak layer is down 80 to 120 cm below the surface. This interface consists of wind hardened snow, facets, a sun crust on solar aspects and surface hoar that is present at and below treeline. Compression tests preformed Friday continue to show planar results at this interface. The mid and lower snowpack are well settled and strong.Variable winds in the past month have created cornices on many alpine ridgelines. They will become touchier as they grow in size, as temperatures rise, and as the strong late-winter sun shines down upon them on clear days.
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.
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.