Regions
Northwest Coastal.
Forecast freezing levels and precipitation amounts are highly uncertain for Sunday. Pay close attention to how much rain or snow falls in your area and be prepared to back off to simple terrain.
Confidence
Low - Timing, track, or intensity of incoming weather system is uncertain on Sunday
Weather Forecast
Saturday night: 5-20cm of new snow with rain at lower elevations / Strong to extreme southerly winds / Freezing level at 1800mSunday: 5-30mm of precipitation / Strong to extreme southerly winds / Freezing level at 2400mMonday: Clear skies / Strong to extreme southerly winds / Freezing level at 2400mTuesday: Trace amounts of new snow / Light variable winds / Freezing level at 1200m
Avalanche Summary
On Friday, warm temperatures and sunshine initiated numerous loose wet avalanches to Size 1.5 on steep solar aspects in the alpine around the Terrace area. Warming also triggered a few deep persistent slabs to size 3 out of steep south facing alpine terrain. Basal facets were though to be the culprit in these events. Looking forward, forecast snow and wind will likely promoted a round of storm slab activity in higher elevation terrain. In areas where rain falls, loose wet avalanches may continue to run in steep terrain .Avalanche and snowpack data is extremely sparse at this time. Please submit your observations to the Mountain Information Network. (MIN)
Snowpack Summary
Up to 5mm of rain fell in the Skeena corridor on Friday night. At higher elevations I suspect snow fell and was shifted by strong winds into wind slabs in lee terrain. In the Bear Pass area where temperatures were cooler, around 15cm of new snow fell down to near valley bottom. These accumulations overlie melt freeze crusts and possibly surface hoar.Another layer of large surface hoar that was recently observed in the Shames area is now buried about 15 cm below the surface. Information on the distribution and reactivity of this layer is limited. Below it, storm snow received last week is gradually settling above a 5-10 cm thick crust (November 23) down roughly 70-100cm. 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. The base of the snowpack is reported to be a mix of facets and melt-freeze crusts..
Problems
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.
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.
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.