Confidence
Fair - Forecast snowfall amounts are uncertain on Thursday
Weather Forecast
Wednesday night: 10-15cm of new snow / Strong southwest winds / Freezing level at about 900mThursday: 10-15cm of snow / Moderate southwest winds / Freezing level at about 1200mFriday: About 10cm of snow / Moderate to strong southwest winds / Freezing level at about 1500mSaturday: 20-30cm of snow / Moderate to strong southwest winds / Freezing level 1600-2000m
Avalanche Summary
A size 2 persistent slab avalanche was remotely triggered from a distance of 10m on Monday. The avalanche failed on the February 10th interface. In addition, numerous natural storm slab avalanches to size 2 were reported at all elevation bands in the region, although I suspect observations have been limited due to steady snowfall. I expect avalanche activity to increase in size and frequency with forecast weather.
Snowpack Summary
A punchy storm slab overlies small surface hoar in sheltered areas, a sun crust on solar aspects and wind slabs at higher elevations. The height of the storm snow may exceed 60cm in some areas, but in exposed terrain these new accumulations have been pushed into much deeper deposits by generally moderate southwest winds. Ongoing snowfall, wind and warming will add to the reactivity and destructive potential of this developing storm slab.There is ongoing concern a mix of weak surfaces which were buried on February 10th. This persistent interface lies between 80 and 140cm below the surface, and includes surface hoar, well developed facets and a mix of hard surfaces which remain widespread at all aspects and elevations. Although natural avalanche activity has tapered-off at this interface, large and destructive human triggered avalanches are still possible, particularly with the increased load of the new snow.For the most part, the mid and lower snowpack are strong and well consolidated.
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.