Regions
South Coast Inland.
Avalanche problems increase with elevation. You may not see wind slabs releasing naturally on Sunday, but they are much more likely to react to cornice fall or human trigger.
Weather Forecast
Sunday: Cloudy with scattered flurries bringing a trace to 5 cm of new snow. Light to moderate southeast winds. Freezing level to 1400 metres with alpine temperatures around -4.Monday: Cloudy with sunny periods and isolated flurries with a trace of new snow. Light southwest winds. Freezing level to 1700 metres with alpine temperatures of -2.Tuesday: Cloudy with scattered flurries bringing about 5 cm of new snow. Moderate to strong southwest winds. Freezing level to 1700 metres with alpine temperatures around -1.
Avalanche Summary
Reports from Friday showed wind slabs releasing to Size 1 with ski cutting in steep lee and crossloaded features as well as loose moist sluffs triggering naturally to Size 1 out of steep terrain.Reports from Thursday showed both natural and skier triggered storm and wind slabs releasing from Size 1-2 in the north of the region. Wind slabs were noted releasing above the melt freeze crust that was buried on March 22. In northern parts of the region, the deeper February weak layers continue to present a low probability / high consequence avalanche danger scenario.
Snowpack Summary
Steady light snowfalls over the week have deposited 25-45 cm of heavily wind affected new snow at upper elevations. Periodic rises in freezing levels to 2000 metres or higher over the same time period have been setting up a series of crust layers (March 20, 22, 23) within the upper snowpack at lower elevations and on solar aspects. A more widespread thick rain crust (March 15) exists up to 2100m and is now buried approximately 45-70cm below the surface. In the north of the region, the February weak layers are 100-140 cm deep and include a buried surface hoar layer as well as a crust/facet layer that appear to be gaining strength. In the southern parts of the region, the mid and lower snowpack are generally well settled and strong.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.