Weather Forecast
Tuesday: Warming, rising freezing levels and strong winds are forecast. Up to 40mm of precipitation is expected with freezing levels up to 1500m later in the day then falling back to 600m. Ridgetop winds will be 80km/hr from the SW. Wednesday: Heavy precipitation continues 25-35mm. Freezing levels near 800-1000m. Thursday: Strong winds will taper off early in the day, few flurries expected as a ridge builds across the region.
Avalanche Summary
Evidence of natural avalanche activity occurred overnight during the storm. Explosive avalanche testing produced slab avalanches up to size 2 on NE and NW aspects. With forecast snow and wind, we can expect to see a continued avalanche cycle.
Snowpack Summary
An additional 20cms accompanied by strong Southerly winds is forming new wind slabs and storm slabs on the upper snowpack. The upper 50-60cms of the snowpack is resting on a variety of older snow surfaces. These surfaces include previous cold, dry low density snow which may have had seen some faceting, old wind slabs, and crusts. Reports indicate it may be particularly reactive between 1700 and 1800m, although I would be concerned about this interface on all steep terrain right now. A rain crust lies buried approximately 30-50 cm below the snow surface at lower elevations (up to around 1800m). Reports indicate the bond at this interface is quite good, although the slick nature of the crust may still provide a sliding layer in some steeper locations. This may be a layer of concern with forecast wind, snow and rising freezing levels to come. Previous concerns about deeper persistent weak layers appear to have diminished. Snowpack depths at treeline are in the region of 260 cm.
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.
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.