Regions
South Coast Inland.
A week of benign weather will allow the snow to gradually gain strength. Use caution around wind loaded slopes where the recent snow may still be reactive to human triggers.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
MONDAY: Mainly cloudy with isolated flurries and 2-5 cm of new snow, light west wind, freezing level rising to around 800 m.TUESDAY: Mostly sunny, light wind, freezing level rising to around 1000 m.WEDNESDAY: Sunny, light to moderate west wind, freezing level rising to around 1300 m.
Avalanche Summary
On Saturday, one natural size 2 slab was observed on a south aspect at 1900 m in the Duffey area and another smaller slab was reported on a steep wind-loaded feature in the Coquihalla area. Dry loose avalanches were reported in steep terrain in the Coquihalla area and wet loose avalanches were observed throughout the region in steep south-facing terrain.On Friday, wind slabs were sensitive to skier triggering to size 2 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.
Snowpack Summary
The Coquihalla picked up a surprise 35 to 45 cm on Friday 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 fell last week. All of the new snow rests on the February 23 weak layer. The February 23 weak layer is now 80 to 120 cm deep in the southern part of the region and about 40 cm deep in northern parts of the region. 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.