Watch for reactive storm slabs to form as the temperatures rise and the new snow settles. Tricky conditions still exist due to a touchy weak layer. Conservative terrain selection is critical.
Weather Forecast
FRIDAY: 10cm new snow through the day, moderate to strong southerly winds, freezing level rising to 1500m. SATURDAY: up to 20cm overnight with lingering flurries through the day, moderate westerly winds, freezing level of around 1500m. SUNDAY: flurries, light westerly winds, freezing level returning to valley floor overnight before rising to 1500m through the day.
Avalanche Summary
A resurgence in storm slab activity is expected as the new snow settles. There is the ongoing possibility of triggering more destructive persistent slab avalanches in isolated open, unsupported terrain features at and below treeline.
Snowpack Summary
Up to 20cm of dry, low density snow fell overnight on Wednesday adding to the 40cm that has fallen in the last week. Cool temperatures have slowed the settlement of this storm snow. Moderate southwesterly winds on Thursday will have formed fresh wind slabs in lee features at treeline and in the alpine. This snow may be sitting on a crust that extends up to 1900m. In the far south of the region the new snow may also be sitting on a layer of surface hoar at treeline elevations. Deeper in the snow pack, the surface hoar layer from early January is now down 80-120cm in most places. Although this layer has become harder to trigger and is variably reactive in snowpack tests, it still has the potential for wide propagations. With that in mind, I would continue to show respect for this layer in steep, open terrain at treeline and below.
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.