Regions
Northwest Coastal.
The incoming storm is expected to deliver more snow (and greater avalanche danger) to coastal areas. Expect new snow to bond poorly with the surface.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
Saturday: Cloudy with flurries bringing 5-15 cm of new snow to higher elevations, increasing overnight. Light rain possible below 1000 metres. Greatest accumulations in coastal areas. Strong to extreme south winds. Freezing level dropping from about 1800 to 1400 metres over the day with alpine temperatures around 0 to -1.Sunday: Continuing wet flurries bringing approximately 10 cm of new snow to the high alpine. Light rain below about 1900 metres. Moderate to strong south winds. Freezing level to 2400 metres with alpine temperatures around +1.Monday: Mainly sunny. Strong south winds. Freezing level to 3200 metres with alpine temperatures of +5
Avalanche Summary
Warm alpine temperatures and sunshine initiated numerous wet loose avalanches to Size 1.5 on steep solar aspects in the alpine around the Terrace area on Friday. Natural slab avalanches icefall releases reached to Size 2.5 in the Bear Pass area. Looking forward, expect new snow accumulations to bond poorly with the crust and surface hoar that form our current snow surface. New snow loading may also begin to overload the December 4 surface hoar layer (now down about 15 cm), where it exists. Please submit your observations to the Mountain Information Network. (MIN)
Snowpack Summary
Snowpack depths in the region remain below seasonal, with recent heavy wind effect creating variable depths of around 110 to 190 cm at treeline elevations in the Shames area. Solar and temperature crusts now exist on the majority of the the surface and surface hoar was observed developing on sheltered aspects above the valley cloud in the Bear Pass area on Thursday. 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. Below it, the basal snowpack is a mix of weaker, sugary snow.
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.