Snow and wind will keep storm slabs touchy, and coupled with the potential for cornice triggers, the likelihood large persistent slabs is expected to increase.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
SATURDAY: Cloudy with 3-5cm of fresh snow accompanied by light to moderate southerly winds. Alpine temperatures reaching -5 C.SUNDAY: Cloudy with another 5-10cm of fresh snow by morning and continued light flurries throughout the day accompanied by moderate SW winds. Alpine temperatures hovering around -5 C.MONDAY: Cloudy with another 5cm by morning and light snowfall throughout the day accompanied by moderate to strong SW winds and freezing levels rising as high as 2000m.
Avalanche Summary
Reports from Thursday include a cornice collapse that triggered a Size 3 slab avalanche directly below in steep, rocky unsupported terrain. Reports from Wednesday include observations recent 40-70cm deep natural storms slab avalanches up to Size 2.5, and a 40cm deep skier triggered Size 1.5 persistent slab avalanche.
Snowpack Summary
5-15cm of fresh snow adds to the 40-80cm of settled storm snow from the past week that is bonding poorly to faceted snow, thin sun crust on steep southerly aspects, as well as surface hoar in sheltered areas in some parts of the region. Touchy storm slabs can be found at all elevations with weaknesses within and under this recent snow. Previous southerly and more recent northerly winds have loaded lee aspects with particularly deep and touchy wind slabs. About 60-120 cm below the surface you'll likely find the mid-February persistent weakness, which is composed of a thick rain crust up to about 1700 m, sun crusts on steep solar aspects, and spotty surface hoar on shaded aspects. Professionals in the region have also warned that a 'threshold load' has been reached above this interface, particularly where it presents as a crust. Some lingering surface hoar weaknesses from January are now down over a metre and the weak mid-December facets are down about 1.5 metres. These deep persistent weaknesses still have the potential to react to human triggers or smaller storm slab avalanches.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.