With plenty of low density snow already available for transport, the southwesterly winds forecast for Friday are expected to drive avalanche activity early in the coming storm.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
FRIDAY: the first wave of a series of storms is expected to hit bringing up to 15cm of new snow through the day, accompanied by light to moderate westerly winds. The temperature at tree-line is expected to range between -5C in the south of the region and -15C in the north. SATURDAY: No snow is expected. Winds will continue to be light from the south and the tree-line temperature will creep up to -5C. SUNDAY: Up to 10cm of snow, moderate to strong south winds, -10C at tree-line.
Avalanche Summary
There have been no reports of recent avalanche activity.
Snowpack Summary
It sounds like good riding conditions out there. Recent variable winds have produced small wind slabs on both south and north aspects. Below tree-line a layer of surface hoar can be found buried down 80 to 130cm. It is of greatest concern in open features such as cut blocks and old burns, at elevations between 1400 and 1800m. Snow pit tests on this interface have been widely variable producing sudden planar, resistant planar and sudden collapse results. The mid and lower portions of the snowpack are thought to be mainly well consolidated.
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.
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.