Vancouver Island Avalanche Bulletin

Valid Until: Saturday 31 December, 2011.

Confidence:  Moderate. While the pattern is clear, exact timing and intensity can easily vary from what is forecast below.
Ratings above are for areas of highest precipitation. Watch precipitation amounts for the area you are traveling in.

Main Concerns: (Avalanche problems)

Wind Slab - Wind slab has been created on weak layers by winds predominantly from the SW. These slabs will continue to form with more new snow and wind in the forecast.

Storm Slab - With sufficient quantities of new snow and snow driven by wind, load will increase on weak layers making natural avalanches likely on all aspects in the alpine and possible at tree line and below.

Weather:

It's been more of the same with a series of frontal systems bringing between 20 and 70mm of water to the island mountains since Monday (greatest amounts on the west coast, lowest on the north and east island with median amounts in the center of the island). All of this precipitation came as snow to the high alpine but rain made it's way up to around tree line for some time. Winds were moderate to strong mostly from the SW to SE. The outlook is for a continuation of the same pattern as follows:

Wednesday/Thursday: one frontal system continues overnight Wednesday before a short break and then another front starting Thursday afternoon. Total accumulations for overnight Wednesday and Thursday 30-50mm. Freezing levels dropping from 1500m Wednesday to 500-900m for Thursday. Winds moderate to strong SW during precipitation and briefly NW during the break between systems.

Friday: Continuation of Thursdays system followed by another break between systems. An additional 10-25mm precipitation. Freezing levels around 900m. Winds moderate to strong SW during the system and again shifting to NW during the break.

Saturday: A short lived ridge of high pressure to bring a mix of could and sun in the morning before the next system hits later in the day. Freezing levels 300-500m in the morning and light to moderate NW winds. Just a trace of precipitation possible earlier in the day with more coming later.

Snow Pack:

The island snowpack varies quite a bit from the east coast to the west and north island. Snowpack conditions described below may or may not apply exactly to the area that you are in so local investigation is important. In the alpine and at tree line thick wind slabs overlie weak faceted snow at crusts. These slabs are easily triggerable by human loads and render easy, planar test results. Areas below tree line which are sheltered from both wind and sun may have surface hoar lurking below. The mid pack is very strong. The base of the snowpack has faceted crystals which are likely to strong to fail in most places though with increasing loads some very specific areas (shallow and rocky in the highest alpine only) may warrant attention.

Avalanche Activity:

Natural and human triggered avalanches to size 1.5 have been observed. Bigger avalanches become possible in the time frame of this forecast as snow and wind continue to build deeper slabs across larger expanses of terrain and bring loads to levels at which they will trigger deeper instabilities.

Travel Advice:

Staying out of avalanche terrain during times of high hazard is your best bet for avoiding getting caught in a potentially fatal avalanche. If you don't know what avalanche terrain is, take an avalanche course to learn to distinguish it. Stick to low angled and well forested slopes and stay away from wind loaded areas near ridge crests and in places which are "cross loaded". Watch for signs of instability in the snow such as natural avalanches, "whumpfing" sounds, cracking, shooting cracks and hollow sounds. Remember to be aware of what is above you and below you: In poor visibility it is possible to be unaware of avalanche terrain primed for release above you and remain aware that even small avalanches can have serious consequences when they drag you into a terrain trap below you such as trees and cliffs.

Prepared by Jan Neuspiel