Confidence is poor due to wildly variable wind slabs and a forecasted Above Freezing Layer that suggests we may not get a refreeze between 1500m and 2800m until Friday.
Weather Forecast
Synopsis: Arctic air is now dominant over all of the South Coast. Warmer air riding up and over the arctic air has created an above freezing layer that should stick around through Thursday evening.Wednesday: Freezing Level: Valley Bottom, Above Freezing Layer 1500 to 2800m; Precipitation: Nil; Wind: Treeline: Light, NE | Ridgetop: Moderate, N.Thursday: Freezing Level: Valley Bottom, Above Freezing Layer 1500 to 2800m; Precipitation: Nil; Wind: Treeline: Light, NW | Ridgetop: Light, N/NW.Friday: Freezing Level: 300m; Precipitation: Trace; Wind: Treeline: Moderate, SW | Ridgetop: Extreme, W.
Avalanche Summary
Numerous wind slab avalanches ran naturally and were triggered by skiers/vehicles on Monday to size 2.5 on SE through SW facing features between 2000 and 2200m.A member of a very experienced ski touring party was caught and carried by an avalanche on an alpine feature near Tenquille lake Monday. Aspect/bed surface unknown at this time.
Snowpack Summary
Strong outflow winds on Dec. 28 left due north slopes mostly wind pressed, some may even be scoured down to the mid Dec. crust. Slabs up to a meter thick can be found on south facing alpine features and some degree of cross loading exists on everything but the most wind sheltered terrain..Three primary layers of concern: Late Dec SH (Surface Hoar): Previously covered by 5 to 15cm and present on all aspects/elevations, distribution post wind event is certainly different, but for the time being I would presume that every slope has it until proven otherwise.Mid-Dec SH: Down 60 to 80 cm, it is becoming harder to trigger, but snowpack tests are still showing that it has potential for wide propagation. It appears to be most reactive in sheltered treeline locations.Early Dec Crust: Down 40 to 100cm and reported to be on all aspects/elevations. In some places its just a crust, other spots feature mixed forms, small grained facets and/or even the above mentioned surface hoar on top of the crust. My gut says that surface avalanches in motion could step down to this crust. The mid pack below this crust contains several old crust layers, but they seem to have gone dormant for the time being.
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.