Regions
Northwest Coastal.
Forecast freezing levels are highly uncertain for Sunday night and Monday; however, warming is expected to drive the avalanche danger. Use extra caution on sun-exposed slopes and limit your exposure to large overhead terrain.
Confidence
Low - Freezing levels are uncertain on Monday
Weather Forecast
Sunday night: 5-25mm of precipitation / Moderate southerly winds / Freezing level at about 2000mMonday: Mainly clear / Moderate to strong southerly winds / Freezing level at about 2000mTuesday: 2-5cm of new snow / Moderate southerly winds / Freezing level at 1700mWednesday: Mix of sun and cloud / Light and variable winds / Freezing level at 2300m
Avalanche Summary
Recent rain, warm temperatures and sunshine initiated numerous loose wet avalanches to Size 1.5 throughout the region. Recent warming and solar radiation also triggered a few deep persistent slabs to size 3 out of steep south facing alpine terrain in the Skeena corridor west of Terrace. Basal facets were thought to be the culprit in these events. Finally, warming was also responsible for a size 2.5 wet slab avalanche that was reported to have failed in the Bear Pass area on Saturday. With precipitation forecast for Sunday night and continued warming on Monday, more loose wet avalanche activity is expected, especially in steep, sun-exposed terrain where cold snow is exposed to solar radiation for the first time. With the forecast warm weather, I'd also consider the possibility of deeper, more destructive slab avalanches.Avalanche and snowpack data is extremely sparse at this time. Please submit your observations to the Mountain Information Network. (MIN)
Snowpack Summary
On Friday and Saturday night about 10mm total precipitation fell 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.