Avalanche danger is expected to remain at Considerable during the forecast cold and clear weather for the end of the year.
Weather Forecast
Clear and cold overnight with alpine temperatures dropping to about -25 and moderate Northeast winds. Winds becoming strong Northwest during the day on Tuesday and alpine temperatures rising up to about -16 under clear skies. Cold and clear with light Westerly winds on Wednesday. Increasing cloud on Thursday with a chance of light snow in the afternoon.
Avalanche Summary
No new avalanches reported. Natural avalanche activity is tapering off as the storm ends and the storm slab settles. Human triggering continues to be likely to very likely due to the storm slab sitting on a hard sliding surface with a weak layer of surface hoar at the interface.
Snowpack Summary
Some new windslab has formed at higher elevations that is 20-40 cm thick, easy to trigger, and may step down to the mid-December surface hoar. The touchy mid-December surface hoar layer is now buried below a 50-90 cm consolidated slab that developed during last weeks storm. Below 2100 m this slab sits on a thick, solid crust/ surface hoar combination and has been acting as a perfect sliding layer. A hard rain crust with facets from early November is buried over 1 m down and is currently unreactive, however; triggering from shallow rocky and unsupported terrain remains a concern.
Problems
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.
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.