There is uncertainty in forecast snowfall amounts Thursday into Friday. The higher end of estimates will be concentrated in the south of the region.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
THURSDAY: Flurries, accumulation 5-10cm / Wind light south / Alpine temperature -10 FRIDAY: Isolated flurries, accumulation 5-10cm / Wind light to moderate southeast / Alpine temperature -10 SATURDAY: Mix of sun and cloud / Wind light west / Alpine temperature -11
Avalanche Summary
A report from just northeast of Nakusp on Monday shows a size 2 persistent slab release on a north aspect at 1800 metres. Another report from Sunday showed a skier-triggered Size 1 persistent slab releasing from a north aspect at 2200 metres.
Snowpack Summary
Last week's storm brought 50-80 cm of new snow to the region. Predominantly northerly winds have since redistributed this storm snow into wind slabs at higher elevations. In sheltered areas cold temperatures have inhibited slab formation. The storm snow lies over a variety of old surfaces, including surface hoar (weak, feather-like crystals), sun crust, and sugary facets. 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 the storm, such as sheltered areas at and below treeline or sheltered northerly aspects in the alpine. 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 90-120cm deep. Recent evidence from adjacent regions suggests it may be reactive in steep, variably loaded terrain features in the alpine.
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.