Regions
South Coast Inland.
More warm, wet, and, windy weather in the forecast means that dangerous avalanche conditions will persist on Monday.
Confidence
Moderate - Freezing levels are uncertain
Weather Forecast
Sunday night: Periods of snow bringing 20-30 cm of new snow. Heavy rain below about 1100 metres, possibly 1600 metres.Monday: Continuing periods of snow bringing 10-25 cm of new snow to higher elevations. Rain below about 1600 metres. Strong to extreme southwest winds Freezing level to 2000 metres with alpine temperatures around 0.Tuesday: Mainly cloudy with isolated flurries and a trace to 3 cm of new snow. Moderate to strong southwest winds. Freezing level to 1200 metres with alpine high temperatures around -4.Wednesday: A mix of sun and cloud with isolated flurries and a trace of new snow. LIght west winds. Alpine high temperatures of -7.
Avalanche Summary
Reports from Saturday showed recently formed storm slabs reactive to skier traffic and ski cutting, producing small (Size 1, 30-35 cm deep) storm slab and loose dry releases. Poor visibility was noted to be limiting observations.On Thursday, two natural storm slab avalanches stepped-down to facets at the bottom of the snowpack and resulted in Size 3-3.5 avalanches. They occurred on north and south aspects between 2000 and 2250 m. The extended period of continuous loading of the snowpack may begin to reactivate deeply buried weak layers resulting in large and destructive avalanches running full path.
Snowpack Summary
Another 10 cm of new snow on Sunday morning brings recent storm totals to 90-120cm. Moderate to strong south winds have been redistributing each day's accumulations into dense storm slabs in lee and cross-loaded features at treeline and above.90-120cm below the surface you'll likely find a few crusts that were buried during the first few weeks of January. Due to limited observations, not much is known about the current reactivity of these layers.The lower snowpack includes the mid-December crust layer. The load of the new snow may tip the balance and reactivate this layer in isolated terrain - particularly in the north of the region where it has shown prolonged reactivity in snowpack tests.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.