Think wind slabs on lee slopes and a persistent slab that seems to be "waking up" on southerly slopes.
Confidence
Moderate - Freezing levels are uncertain on Friday
Weather Forecast
FRIDAY: Cloudy with isolated flurries / Light southeast wind / Alpine temperature -7 / Freezing level 1000m SATURDAY: Cloudy with isolated flurries / Light southeast wind / Alpine temperature -8 / Freezing level 900m SUNDAY: Mix of sun and cloud / Light southeast wind / Alpine temperature -12 / Freezing level 500m
Avalanche Summary
On Wednesday a size 2 remotely triggered (from a distance of 10m) persistent slab avalanche was reported to run on surface hoar sitting on a crust that was buried mid February. This was on a southwest aspect at 1800m. Other recent avalanche activity has consisted of mainly wind slabs and loose dry in the size 1-1.5 range but up to size 2. These were either naturally occurring or intentionally triggered. More interesting avalanches included a re-loaded bed surface where an avalanche previously released on the Nov crust and the "newly awoken" Feb 14 crust found on solar aspects. Deep persistent avalanche activity has become less frequent over the past week.
Snowpack Summary
Around 40 to 60 cm of recent storm snow is being redistributed into deeper, reactive slabs in wind-exposed terrain. Below this is a layer buried mid-February that presents as a sun crust on solar aspects, and spotty surface hoar on sheltered slopes. This layer looks most concerning on on solar aspects where it's associated with with small facets or surface hoar above.There are several deeper layers in the mid-pack that have shown signs of improving but remain on the radar as having a low probability of triggering yet a high consequence avalanche if they are triggered. We're talking about surface hoar layer buried back in December and January. Near the base of the snowpack is a November crust combined with loose sugary snow. These layers may "wake-up" with strong inputs such as sustained warming, sustained snowfall, large triggers (e.g. cornice fall, smaller avalanches coming down from above); human triggering is also possible in shallow snowpack areas with variable snow depth and convoluted 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.