The region has seen higher snowfall amounts than weather forecasts have indicated. A cautious approach is recommended in the coming days as temperatures gradually rise and the recent storm snow settles and consolidates more rapidly.
Confidence
Moderate - Freezing levels are uncertain on Tuesday
Weather Forecast
SUNDAY: Mix of sun and cloud / Light west wind / Alpine temperature -13 MONDAY: Mix of sun and cloud / Light to moderate west wind / Alpine temperature -5 TUESDAY: Mix of sun and cloud / Moderate northwest wind / Alpine temperature -2, possible temperature inversion
Avalanche Summary
Recent reports show natural several storm snow avalanches to size 2 at tree line and in the alpine on all aspects. There have been a few reports of remotely (from a distance) triggered persistent slab avalanches to size 2 on northerly aspects between 1700 and 2000m. Consider the potential to trigger persistent slabs as the recent storm snow settles more rapidly on top of the Mid-December persistent weak layer with gradually warming temperatures in the coming days.
Snowpack Summary
30-50cm of low density new snow has buried a recently formed layer of weak feathery surface hoar and/or sugary facets. A layer buried mid-December that consists of surface hoar, sun crust and/or sugary facets is now down approximately 50-70cm.The bond at this old snow interface is of critical importance in areas where the overlying snow has consolidated into a slab. The most concerning areas are those that saw pronounced surface hoar development before mid-December, such as sheltered areas at and below treeline, sheltered northerly aspects in the alpine, or anywhere the surface hoar formed on top of a sun crust. Recent snowpack tests show wide ranging reactivity on this weak layer but suggest that it may be most reactive on northerly aspects. A rain crust that formed in late November is now buried 80-120cm deep. A report from last week in the southwest end of this region suggests it may be reactive in steep, variably loaded terrain features in the alpine.
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.