Vancouver Island Avalanche Bulletin

DANGER RATINGS (Make sure you understand the danger level meanings)

Outlook	Monday	Tuesday	Wednesday
Alpine	CONSIDERABLE +	CONSIDERABLE	HIGH
Treeline	CONSIDERABLE	CONSIDERABLE	HIGH
Below Treeline	MODERATE	MODERATE	CONSIDERABLE

Confidence: Good ~ except precipitation amounts for Monday and Tuesday will vary across the forecast region with nearly double the amounts for the North Island possible. Monday's winds could produced loclized windslabs as well.

 Main Concerns:

• Soft slab from new snow and 48 hour storm snow
• Wind slabs Alpine & Tree Line
• Cornice Fall and or Steep slopes shedding

Weather:

Last Friday's storm was memorable, with 40 to 50 mm precipitation very strong winds and relatively cool temps. The weekend weather backed off to flurries giving another 10 to 20 cm snow and some clear breaks with cool temps and winds that were comparatively manageable from the South and West.

The outlook for the start of the week is continued winter with 500m freezing level for the forecast period: Expect 15 cm plus by Monday AM and continued flurries for the day (10 cm more) , with Light to Moderate winds. For Tuesday light winds and flurries. The next storm arrives Wednesday with heavy snow and winds picking up again to strong SE S or SW depending on local.

Avalanche Activity:

Friday's Natural cycle was un-witnessed due to the severity of the storm.  Saturday some areas in the South Coast Region saw Size 2 to size 3 with up to 2 m deep windslabs with avalanche control! Cornice fall debris and left over hard wind slab chunks were also reported. Maybe the April 02 2010 storm caught people's attention?

Snowpack:

The Alpine elevations have gained a fair chunk of snow Through March and early April.  Terrain begins to fill in and boundaries between avalanche paths are less distinct. Lee Aspects NW through East are much deeper near terrain breaks and ridge tops; this process not only builds cornices but steepens the slopes near their tops.  These factors promote larger avalanches laterally and may promote easier triggering due to steepness of slopes. 

The old snow layers from January and February are no longer much of a concern as they gained rain and then refroze in March. Our concerns today are more typical for the Coast; storm snow and windslabs with over developed cornices and snow plastered on some steeper slopes.  The depth and consistency of the windslabs varies quite a bit due to the extreme and changeable winds; 25 cm and quite stiff cross loaded slabs to 1.5 meter deep wind slabs with softer and stiffer layers providing some shears in the Easy to moderate range closer to the surface. Most of the upper snowpack is settling and bonding fairly well deeper down.

In the worse case right now a cornice drops and triggers a large slope into the first wind slab which then steps down to the other older slabs above the crusts. This could be up to 3 meters deep but not likley with out warming or more load...

Consider using SIMPLE or CHALLENGING TERRAIN with lower angle < 35 degree slopes and more supportive shapes and less wind loading exposure.

Travel advisory:

Human Triggering is Probable to Possible for Monday and improving for Tuesday: New snow instabilities exist and would worsen with warming or sun.  Localized Wind Slab on Lee and Cross-loaded slopes exist on East through North through W aspects at and above Tree Line. Wide spread new Cornice formation exists NW through East and is very acutly formed at this time.. The thinner wind zone crossloaded features are likely to be more sensitive to human triggering as are steeper slopes and stress points or convex areas. By Wednesday Human Triggering may be Likely to Probable at and above Treeline.

Outlook:

Winter fest continues for the VancouverIsland Ranges; more snow over night Sunday gives way to a windy day with some intense flurries Monday. Tuesday looks pretty good with lighter perhpas Westerly winds and flurries. The next storm arrives Wednesday with more 30 to 50 cm snow and moderate to strong winds generally South. The good news is the  500m freezing level for the forecast period. , and lower with any over night clearing.