The chance of triggering a persistent slab has decreased, but the consequences remain high.
Confidence
Fair - Intensity of incoming weather systems is uncertain
Weather Forecast
Snowfall peters out on Saturday before a second pulse of snow arrives on Sunday and continues through Monday, bringing 10-20 cm. Winds are generally light until Sunday night, when they rise to moderate westerly. Freezing level is at valley floor.
Avalanche Summary
There was a widespread avalanche cycle earlier in the week in response to the warm storm, with a round of persistent slabs. Natural activity has now eased, but a few cornice drops triggered storm slabs on Thursday.
Snowpack Summary
New snow is falling on a supportive crust, found below about 1900 m in the north and 2100 m in the south. At higher elevations, recently formed wind slabs may be found lee to the south-west. Recent warming and subsequent cooling have helped strengthen the mid-January surface hoar layer, but it still remains a concern, especially at high elevations. The mid-December surface hoar layer is 80 to 140cm below the surface and appears to be slowly gaining strength. Basal facets could be triggered with large triggers like cornice fall in specific terrain.
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.