This Bulletin Valid Until: Monday December 25th, 2017 @ 6 pm. 

Main Concerns: (Avalanche problems)

Wind Slab -  Strong NE through W winds have redistributed Tuesday's storm snow in the alpine and at treeline elevations. This redistribution has been highly variable and has resulted in deposits of both stiff and soft slabs on E through SW aspects. These pockets of wind slab overlie a crust which may act as a sliding surface and will be loaded further with new snow and wind forecast for Sunday. The elevated hazard rating reflects areas within the forecast region that see greater totals of predicted snow. Natural avalanches are possible and human triggering is likely. Large alpine features where these conditions exist have the potential to produce large avalanches (size 2+).

Travel/Terrain Advice: Avoid recently loaded slopes and rollovers in the alpine and at treeline. Be aware that smaller hard slab avalanches have the potential to have higher consequences than low density slabs. Watch and listen for signs of instability such as shooting cracks or whumpfing. Cold air and snow temperatures will contribute to slower bonding and settlement and the chance of a lingering avalanche problem.

Past Weather: A strong winter storm on Tuesday delivered snow totals up to 40 cm on eastern Vancouver Island with the western and northern areas seeing less accumulation (10-15 cm). Directly following the band of precipitation, strong NE through W winds stripped windward slopes back down to the old crust and deposited the storm snow into lee terrain and also lower elevations. Wednesday and Thursday brought continued cold temperatures and low freezing levels and little to no precipitation.

Avalanche Summary: On Tuesday numerous small soft storm slabs were reported at treeline on NW through NE aspects on all sufficiently steep slopes in the Mount Washington area. These avalanches were touchy to very touchy to ski cutting and were failing on the old crust that was buried 20-40 cm. One natural slab avalanche was observed at treeline on a SW aspect failing at the crust. On Wednesday a small wind slab was triggered at treeline on a SE slope by a snowmobile. Numerous snowmobiles were observed high marking at treeline on an alpine-like feature on a N-NW aspect with no result. 

Snow Pack Description:  

Surface - Highly variable distribution of recent storm snow. Exposed crust in all windward (NE-W) alpine and treeline terrain. Pockets of stiff and soft wind slab in lee and protected areas. Sheltered terrain below treeline has low density dry snow of up to 40 cm on the mid December crust. 

Upper - Variable dependent on aspect and elevation. 10-40 cm of new snow overlies the old crust layer and has shown poor signs of bonding.

Mid - Well settled.

Lower - Well settled.

Weather Forecast: An arctic ridge of high pressure bringing clear skies and cold outflow winds will dominate Friday and Saturday. Sunday will see a trough of low pressure break through the ridge and bring precipitation to the coast. Cold temperatures, low freezing levels, and light to moderate winds from the SE will accompany the system.

Fri - 0-3 cm of snow. Winds 30-15 km/h northeast.

Freezing levels of 0-800 m

Sat - Trace amounts of snow on the north and south Island. Winds from the southeast 17-40 km/h.     

Freezing levels of 0-290 m

Sun - 5-20 cm of snow with greatest amounts in south and east regions.  Winds southeast 15-40 km/h veering to 10-18 km/h northwest.

Freezing levels of 0-600 m

Prepared by Dan Goodwin