We're dealing with a complex snow pack and a significant warming trend. Solar radiation will drive the avalanche conditions. Expect avalanche hazard to rise rapidly when the sun comes out.
Confidence
Low - Timing or intensity of solar radiation is uncertain on Monday
Weather Forecast
No precipitation is expected for the forecast period. A strong temperature inversion will develop early on Monday with an above freezing layer forming in the alpine as warm air overrides cool air trapped in the valleys. Valley cloud will linger although there is some uncertainty as to how high it will reach. MONDAY: clouds in the alpine clearing through the day, freezing level rising to 3500m, light westerly winds. TUESDAY: sunny in the alpine, a freezing level of 3500m, moderate westerly winds. WEDNESDAY: sunny with scattered clouds, a freezing level of 2800m, moderate westerly winds.
Avalanche Summary
We have limited observations from upper elevations however fresh wind slabs were reported to be reactive to ski cutting on Saturday. In the north of the regions conditions are likely to be similar to K-country right now where several large (size 2-3) skier triggered avalanches released in wind loaded features over the weekend.
Snowpack Summary
Strong south west winds have resulted in widespread wind effect, forming deep stiff wind slabs at treeline and above, as well as significant cornice growth at ridgeline. In some areas you may find a supportive crust down 30cm that extends up to around 1900m. A layer of buried surface hoar can be found between 50 and 100cm down and remains a concern. The snowpack rests on a weak crust/facet layer from early December.
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.