Lingering wind slabs and large weak cornices are expected to be reactive to human-triggering on Monday. Use increased caution in wind affected terrain.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Light snowfall is expected Sunday overnight before a weak ridge of high pressure dries things out Monday morning. A substantial storm system is then expected to reach the south coast on Monday afternoon or evening. 5-10cm is expected Sunday overnight with freezing levels around 1400m and moderate southwest winds in the alpine. 5-10cm is possible Monday afternoon with freezing progressively climbing to around 1800m by Monday night. Another 20-40cm is forecast for Monday overnight with strong southwest winds in the alpine. Tuesday is forecast to be mainly dry with light alpine winds and afternoon freezing levels around 1500m. A weak storm system is forecast for Wednesday with freezing levels around 1800m.
Avalanche Summary
On Saturday, ski cutting produced size 1-1.5 soft slab avalanches up to 30cm thick in lee and cross loaded features in the alpine and at treeline. Explosives released cornices size 1-2 in the alpine. Rain-soaked lower elevations are unlikely to see much in the way of avalanche activity, but wind slab avalanches will continue to be reactive to human-triggering at higher elevations with ongoing snowfall and wind continuing overnight Sunday. Cornices are reported to large and fragile, and may fail under the weight of a person.
Snowpack Summary
Recent warm temperatures left us with moist snow up to around 1800 metres. Subsequent cooling has left new crusts in many areas. Wind slabs are forming at higher elevations. Cornices are reported to be huge and collapse has become more likely with additional loading and high freezing levels. About 50-90cm below the surface, you'll likely find a rain crust which formed on January 28th. This crust is widespread and exists up to about 2100m. Where it still exists, the mid-January surface hoar layer may be found between 130 and 200 cm below the surface. The combination of warm temperatures and subsequent gradual cooling is making avalanches failing on these deeper layers unlikely.
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.