Strong winds and the potential for heavy snowfall will change the landscape and increase the avalanche danger rapidly. New windslabs will be touchy, and the increased load may awaken midpack layers of concern.
Weather Forecast
Steady snowfall overnight on Wednesday, with models predicting anywhere from 6mm to 35mm through to Thursday evening with strong SW ridgetop winds. After this, precipitation is expected to taper, and winds to moderate.
Snowpack Summary
10-15cm of snow from Jan 10 has blown into thin slabs TL and above. Midpack is faceted with several distinct crusts in the mid to lower snowpack. There is a layer of concern (Dec 15) composed of facets and surface hoar that can be found down approximately 15-30cm. This layer has been active in isolated areas, producing slab avalanches to size 2.
Avalanche Summary
Limited visibility, but one report of a size 2 loose dry avalanche on Mt Wilson that originated in the alpine and ran 400m to the forest below.
Confidence
Forecast snowfall amounts are uncertain on Thursday
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.
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.