Triggering large persistent slab avalanches is a serious concern this weekend. Conservative terrain choices are strongly recommended.
Multiple weak layers have become reactive with the additional load of storms earlier this week. They are mostly composed of surface hoar and facet layers found between 60 and 120 cm deep, and have produced large avalanches that are propagating across terrain features. Most activity has been observed between 1800 and 2200 m.
A significant natural avalanche cycle occurred between December 26 and 28th that included large and very large (size 2 to 3) storm slab and persistent slab avalanches. While natural avalanche activity has slowed down, we continue to see notable human triggered avalanches.
On Thursday, there were multiple remotely triggered size 2 and 3 persistent slab avalanches in Bonnington and Kokanee areas. These occurred on north and east facing slopes between the elevations of 1800 and 2200 m. Although just outside the boundary of this forecast, the photos in this MIN report illustrate the type of terrain where these avalanches are occurring. The failure layers were typically 60 to 80 cm deep and included both of the persistent weak layers discussed in the Snowpack Summary.
Looking ahead to the weekend, triggering large persistent slab avalanches will remain a serious possibility at treeline and alpine elevations.
A dusting of new snow is falling on top of settled snow from the December 26th storm. This storm left 30 to 40 cm of heavy snow above a rain crust (that extends up to 2000 m). While the recent snow has shown signs of settling and strengthening, deeper weak layers have shown continual signs of instability. The two prominent layers of concern are a 50 to 70 cm deep layer of surface hoar and sun crusts that was buried in mid-December and an 80 to 120 cm deep layer of surface hoar and facets that was buried in mid-November. Both of these layers have been most reactive between 1800 and 2200 m.
Friday night
Light snowfall with trace amounts over the Monashees and up to 5 cm in the Selkirks and southern Purcells, 20 km/h wind from the southwest, treeline temperatures around -5 °C.
Saturday
Cloudy with very light snowfall, trace accumulations, 20 km/h wind from the southwest, treeline temperatures around -5 °C.
SundayPartly cloudy with sunny breaks in the afternoon, no precipitation, 20 to 30 km/h wind from the northwest, treeline temperatures around -5 °C.
MondayMix of sun and cloud, no precipitation, light wind, treeline temperatures around -7 °C.
More details can be found in the Mountain Weather Forecast.
