Vancouver Island Avalanche Bulletin

Valid Until: Saturday 07 January, 2012.

Confidence:  Good. Hazard ratings above are for areas of highest snowfall.

Main Concerns: (Avalanche problems)

Wind Slab - Widespread Wind slab has been created in the alpine by winds from the SW through to SE in the lees of ridges and in cross loaded features. Fresh slabs will be formed in the alpine and at tree line overnight Wednesday.

Persistent Slab - Instabilities deeper in the snowpack in the alpine and at tree line which have not failed yet during our current storm may still be primed for trigger by the extra load of a person.

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

Weather:

The island alps were soaked by between 90 and 200mm of water over the past two days. Freezing levels made it up to about 300m above tree line at times meaning that about half of this came as rain to below tree line. Winds were moderate to strong from the SE through to SW.   The outlook is as follows:

Wednesday night/Thursday: 10-35mm of precipitation most of it before Thursday morning. Freezing levels dropping through 1100 to 6000m. Winds light gusting to as high as strong from the SW and W.

Friday: 5-10mm of precipitation. Freezing levels 500-800m. Winds light gusting to as high as strong from the SW and W.

Saturday: Watch for the approach of our next front with rising winds, freezing levels and precipitation later in the day.

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. Snowpack 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 and at tree line. Rain has soaked the surface of the snow pack today up to tree line. Below the storm snow, weak facet/crust layers have been the failure plane for avalanches during the current storm cycle and likely persist in places. 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:

Given the conditions over the past two days we have no observations from the alpine but are certain that a natural avalanche cycle took place. Avalanche control work at Mount Washington produced avalanches to size two running the full length of their path.

Travel Advice:

Though precipitation is slowing and natural avalanche activity will taper off, there will be plenty of wind slab in the alpine primed for trigger by humans and possibly "stepping down" to facet/crust weaknesses deeper in the snowpack creating large avalanches. Travel in avalanche terrain in the alpine is not recommended without advanced training and extensive experience. At tree line new slabs will form overnight Wednesday and early Thursday. Careful route finding by experienced travelers will be necessary to avoid hazard. Stay out of wind effected features and be aware of what is overhead.

Prepared by Jan Neuspiel