Regions
Banff Yoho Kootenay.
Happy New Year! New Years day looks to be cold and windy, but by the time you've recovered from New Years Eve, we should be into another storm cycle!
Weather Forecast
A ridge will bring cold dry conditions for the first day of 2019, and an incoming system will bring strong NW winds in the alpine. Fortunately, this system will also bring snow on Wednesday/Thursday. Precipitation amounts will start light, but forecasts are calling for 20-30 cm on Thursday, with the greatest amounts to the west and north.
Snowpack Summary
Wind effect exists in the alpine and at treeline. Below treeline, the surface is faceted powder. This overlies the Dec. 10th layer of facets and depth hoar which is down 60-100 cm. In thin snowpack areas, the Dec. 10th layer is mixed in with the basal facets and October crust. In thicker areas, it is a distinct layer, with a stronger snowpack below
Avalanche Summary
No new avalanches observed on a field trip on the Icefields Parkway today, but good visibility highlighted more naturally triggered avalanches up to size 2.5 out of steep alpine terrain from the storm on Dec. 29th. These seemed to be on all aspects, and running on the Dec. 10th layer and stepping down to the ground in thin areas.
Confidence
Timing, track, or intensity of incoming weather system is uncertain on Thursday
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.