Watch for new wind slab development on Saturday. Forecast snowfall amounts are uncertain, so pay close attention to how much snow falls in your area, and choose terrain accordingly.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Saturday
Weather Forecast
Up to 12cm of new snow is forecast to fall on Saturday with another 10cm possible in the overnight period. Generally light accumulations (~5cm) are forecast for Sunday and Monday. Ridgetop winds should be moderate from the south on Saturday, becoming light on Sunday and Monday. Freezing levels should sit at about 1800m on Saturday, and then drop closer to 1500m for the rest of the forecast period.
Avalanche Summary
On Thursday there was a widespread round of natural storm slab activity (mostly in the size 2 range with some results to size 2.5) in response to new snow and strong winds. In one case a size 3 persistent slab avalanche was remotely triggered on an east-facing slope at 2230m. This points to the ongoing touchy persistent slab problem in some areas. More wind slab activity is expected with wind and snow forecast for Saturday. Although naturally triggered persistent slab avalanches are becoming less likely, human triggering remains a very real concern in some areas.
Snowpack Summary
Snowfall accumulations on Thursday were in the 10-20cm range. Strong southerly winds redistributed these accumulations into touchy wind slabs at treeline and in the alpine. 60-90cm below the surface you'll find a persistent weak layer comprised of weak surface hoar, and/or a thick crust. This layer continues to produce easy to moderate sudden planar shears in snowpack tests, and has been responsible for a number of increasingly isolated yet very large avalanches over the last few days.
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.
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.