Regions
Northwest Coastal.
Continued warming and precipitation is adding stress to the snowpack and driving the danger rating.
Confidence
Moderate - Freezing levels are uncertain
Weather Forecast
Tuesday: Mainly cloudy with light snow in the alpine and rain showers below. Ridgetop winds moderate from the southwest. Alpine temperatures near 1 degree and freezing levels 1700 m.Wednesday: Mainly cloudy with isolated showers. Ridgetop winds light to moderate from the south. Alpine temperatures plus 5 degrees and freezing levels rising to 2200 m.Thursday: Snow amounts 10-20 cm in the alpine and rain below. Freezing levels near 1700 m. Ridgteop winds light with strong gusts from the south.
Avalanche Summary
On Sunday, rain and warmer temperatures initiated numerous natural loose wet and storm slab avalanches up to size 1 throughout the region. On December 7th and 8th a few deep persistent slabs to size 3 out of steep south facing alpine terrain in the Skeena corridor west of Terrace were reported. Basal facets were thought to be the culprit in these events. The Bear Pass area also saw a size 2.5 wet slab avalanche on Saturday. The deep persistent slab is something to keep on your radar, especially with more weather in the forecast.
Snowpack Summary
The past couple of days brought up to 15 mm total precipitation in the Skeena corridor. Given the mild temperatures, I suspect most of that precipitation fell as rain. At alpine elevations snow likely fell and moderate to strong winds are expected to have formed wind slabs in lee terrain. In the Bear Pass area where temperatures were cooler, around 30cm of new snow fell. These accumulations overlie melt freeze crusts and possibly surface hoar.About 70-100cm below the surface you'll likely find a 5-10 cm thick crust which was buried on November 23. Another layer of surface hoar (November 11) continues to be observed down approximately 140 cm in the Bear Pass area, showing some signs of improved bonding. The widespread crust/facet interface that was buried at the end of October can now be found 90-160 cm deep.
Problems
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.
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.