Vancouver Island Avalanche Bulletin

Valid Until: Monday 09 January, 2012.

 Confidence:  Fair. Uncertainty about precipitation amounts and freezing levels. Danger ratings above are for areas of highest precipitation and wind.

Main Concerns: (Avalanche problems)

Wind Slab - Widespread Wind slab has been created in the alpine and at tree line in the lees of ridges and in cross loaded features from the NW to the SE.

Persistent Slab - Instabilities deeper in the snowpack in the alpine  which date from mid November have significant depths of snow on them where they have not failed in recent storms and could produce large avalanches in those areas. While not widespread they could be triggered from thin slab areas, from heavy triggers such as cornice falls, or from wind slab avalanches stepping down to the deeper weaknesses.

Storm Slab - Weaknesses within and under recent and new storm snow in the alpine are susceptible to natural and human triggers.

Loose Wet: avalanches are possible below tree line on Sunday with rising freezing levels and rain falling on precious storm snow.

Weather:

Since freezing levels dropped on Wednesday and rain turned to snow at all elevations again we have seen between about 2 and 20cm of snow on the island mountains (greatest amounts on the north island). Winds have been strong enough to move snow and to form slabs where there is snow available for transport. Freezing levels have remained low. The outlook is as follows:

Friday night/Saturday: 10-15mm of precipitation. Freezing levels 700m rising to 1400m by the end of the day. Winds moderate to strong SW.

Sunday: 20-40mm of precipitation. Freezing levels continuing to rise to 2000 meters or more. Winds strong SW.

Monday: 5-15mm of precipitation. Freezing levels dropping from 2000m down toward 1000m and below. Winds lightening and turning NW.

Snow Pack:

The island snowpack varies quite a bit from the east coast to the west and north island and is more complex than many are accustomed to seeing on the island. Snow pack conditions described below may or may not apply exactly to the area that you are in so local investigation is important. Wind slabs have been formed and continue to form in the alpine all over the island and at tree line as well on the north island. Rain has soaked the surface of the snow pack on Wednesday up to tree line. Weak facet/crust layers have been the failure plane for avalanches during the last storm cycle but likely persist in places in the alpine. The mid pack is strong. Basal weaknesses are not likely a concern in the island snowpack anymore except perhaps in rare places in the highest alpine with shallow snowpack and smooth ground cover.

Avalanche Activity:

Evidence of wet snow avalanches has been observed on the east and north island below tree line from the rain event of Wednesday.

Travel Advice: In the alpine and at tree line in places which had enough snow and wind choose conservative lines and watch for clues of instability such as cracking and shooting cracks. Assess conditions continually as you travel. Always be on the lookout for wind slab and avoid freshly wind loaded features. Be aware that cornices have formed and are both hazards in their own right but can also act as large triggers to avalanches and are difficult to predict. Skiing is good below tree line for Saturday but things will turn again with precipitation, rising freezing levels and rain on Sunday making hazard high again in the alpine and likely considerable at tree line as new loading by either snow or rain lands on existing weaknesses.

Prepared by Jan Neuspiel