Avalanche danger will be greatest in the band at and above treeline where rain falls on previously dry snow which may lie above an older crust.
Confidence
Poor - Due to the number of field observations
Weather Forecast
Synopsis: A southerly flow will generate widespread precipitation over the southern interior Tuesday and Wednesday before a weak ridge ushers in drier conditions on Thursday. Temperatures will remain warm through the first part of the forecast period.Tonight and Tuesday: Moderate precipitation - up to 15 cm of snow at upper elevations / Moderate southerly winds / Freezing levels between 2000 and 2200m.Wednesday: Light precipitation / Moderate westerly winds / Freezing levels falling to between 1500 and 1700mThursday: Sunny with cloudy periods and a chance of flurries / Light southwesterly winds / Freeing levels around 2000m
Avalanche Summary
Small slabs have been recently triggered naturally and by skiers in areas where the upper snow is moist and sits above a crust. At lower elevations and on solar aspects small to large loose wet avalanche continue to be triggered on steep slopes. Cornices collapses have been reported during periods of daytime warming. Occasionally these heavy triggers have caused large deep slab avalanches on the slopes below.
Snowpack Summary
Moist snow or a fresh crust may be found on the surface on slopes that have seen recent sun. Between 10 to 30cm of snow overlies several widespread melt-freeze crusts on all but high elevation North aspects. Wind slabs can be found in lee features on N and E aspects in the Alpine.Several persistent weak layers exist in the snowpack of the region:- The mid-March sun crust/surface hoar layer down 50-80cm and the early-March crust/facet/surface hoar layer down around 80-120cm seem to be inactive.- The mid-February crust/facet/surface hoar combo is typically down 150 - 200cm. Human triggered avalanches on this layer are unlikely. Larger triggers such as cornice fall, a smaller avalanche in motion or prolonged warming could wake this layer up, resulting in very large and destructive avalanches.
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.