Regions
South Coast Inland.
We're into a period of HIGH danger with rapid loading of the snowpack on Wednesday into Thursday: rain to treeline and heavy snow in the alpine.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
Warm and wet still on Thursday. Cooling with isolated flurries on Friday, and improving for Saturday. THURSDAY: Rain or wet snow (25-40 mm / cm) with even higher amounts possible for the Coquihalla / Moderate to strong southerly winds in the afternoon / Freezing level around 1600 m. FRIDAY: Mostly cloudy with locally heavy flurries possible (5-15cm) / High temperatures to -1 Celsius / Light westerly winds / Freezing level around 1200 m. SATURDAY: Cloudy with sunny periods / Ridge winds light southerly / Freezing level around 900m / High temperatures to -2 Celsius.
Avalanche Summary
Limited observations during this storm.In the Duffey Lake zone a Size 2.5 deep persistent slab was reported running on a south-southwesterly aspect near 2200m, likely triggered by solar warming on Monday or Tuesday.
Snowpack Summary
In the Duffey Lake area 25 cm of snow fell on Tuesday in to Wednesday. In the south (Coquihalla) we had moderate southerly winds and heavy rain above 1600m on Tuesday night (and rain to 2000m during the day Wednesday). This new rain (or snow higher up) sits on either wind slabs in the alpine or temperature crusts at treeline and below, especially on east and south aspects. Both of these surfaces will be good sliding layers for future snowfall. The mid-December facets down 130-160 cm still remain a concern especially in shallower snowpack areas in the Duffey, Hurley and/ or South Chilcotins. These deeper weaknesses warrant monitoring, especially with the warming and extra loading this week. In southern areas (Coquihalla), the lower snowpack is reportedly well settled (stronger), than it is to the north.
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.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.