Vancouver Island Avalanche Bulletin

Valid for end of season period.

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

Outlook
Alpine	Still a bit wintery especially North aspects
Tree Line	Spring is setting in.
Below Treeline	below threshold

Confidence: The forecast accuracy is diminished his time of year due to lack of field information. Our forecast product relies on weather data, visual scans with high power binoculars,  and weekly visits to the mountains. 

Weather can spike the Hazard 'for a period of time' ; such as  Sun, Rain, Snow, Wind, light cloud cover during day, which causes a green house effect.  Further warming problems develop when cloud over night can prevent freezing of the surface and high prolonged above freezing temperatures persist making the snowpack Slushy or ISO THERMAL.

Main Concerns:

• Wet loose surface avalanches. (Potential Natural Trigger)
• If storms materialize * Wind Slab in Alpine, on leeward aspects West, North and to East. (North and West Isle)
• Cornice Fall above 1700 m, North West North North East East aspects (potential large natural trigger).
• Wet New and Old slab and or deeper wet slab potentially stepping down into February or January layers.

Avalanche Behavior in Spring:  A couple of things do occur in the spring that are worth mentioning:

1. Change happens Fast:    One minute a supportive crust the next slush. Many scenarios are possible but expect rapid change in stability as the temperature and other localized factors influence.
2. Entrainment:      Snow once Isothermal can be picked up by the original starting zone snow or cornice piece, this is called 'Entrainment'. Entrainment potential increases as the snow looses strength and this process greatly increases the volume of snow in involved in an avalanche. 
3. Distance avalanches travel:      Higher water content snow in spring avalanches can exceed normal run outs. The path the debris follow is typically more confined and follows 'Drainage' type features and does not usually travel as fast.
4. Packs a punch:     High water content snow and older deeper layers of the snowpack will typically have a higher water content or density. This means that the debris is heavier, will likely be much harder to dig if it sets up hard (normal).
5. Random Natural triggers:     Avalanche activity may taper right off and lull you into over confidence and then wham! The random large natural trigger cornice or old slab lets go and more snow often releases with it.

Weather:

 

Avalanche Activity:

 

Terrain Discussion: 

Now it is all about timing and imagination: Example: could the cornice over there collapse, trigger the slope below, step down into firmer snow and propagate horizontally into the terrain you are on?

Travel Advisory: If you are deeper than your ankles in slush the snow is not to be trusted.

General Spring time advice: Watch the temperatures and sun and back out before the heat sets in. This time of year the sun, rain and above freezing temperatures are common. This brings the possibility of rapid temperature increases and changes in the snow cover. Natural triggers such as cornice, tree bombs could be active at this time. Human Triggering is unlikely when frozen and Possible to Probable if sudden or prolonged melting or rain occurs. Caution with Travel on or below cornices.   Caution Solar aspects during day warming. Keep good track of your surroundings as large natural triggers could start slides high above you or trigger and propagate  horizontally.

Outlook:

Spring and winter mixing, spring wins in the end.

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

Outlook	Monday	Tuesday	Wednesday
Alpine  1560 m 2200 m	*MODERATE	MODERATE	MODERATE
Treeline	MODERATE	MODERATE	LOW
Below Treeline	LOW	LOW	LOW

Confidence: Good. (Except precipitation amounts and timing. Expect a surge of moisture Monday more West to Central Island South 25 to 30 mm. This could spike the local area Danger Ratings, Forecast if this falls in the form of rain and exceeds 25 mm.

* Timing and Distribution of Hazard during 'Spring' or 'Melt/Freeze' period 'ISO Thermal' period: Key factors to monitor and observe:

• Air Temperatures
  
• Affects of direct Sun
  
• Snow surface conditions (Snow Temperatures ISO Thermal conditions)
  

 Main Concerns:

• Cornice Fall                                                           Any aspects except South.
• Loose Wet surface slides                                  Widespread
• Deep slab on February crusts                        Alpine Leeward

WEATHER

This past few days and week 'Above Freezing Temperatures' have persisted 'At and  below Tree line' (2 degrees C to 5 air and higher on solar aspects rocky areas . Some nightly refreezing has taken place at higher elevations and specific cool aspects.  Precipitation came in the form of drizzle and mixed rain/snow and we saw less than 10mm for the past 3 three days. Wind was not a big factor switching from South to West and a bit calm North.

Sunday eve into Monday AM steady showers with some stiff South winds, 20mm plus more showers expected into Tuesday*. Freezing levels drop a bit by Wednesday until the sun comes out. The Light to Moderate winds start South Mod and switch West by Later Monday hey should ease to the West North West by Wednesday  .

Avalanche Activity:

Primarily surface instabilities, wet loose surface avalanches and continued cornice falls, some as large as size 2.

Snowpack:

A Melt Freeze cycle is wide spread. Over night refreezing ranges from not freezing a lower elevations to freezing lightly to freezing a little harder up high. ISO-thermal is the term used to describe snow that has turned to slush and is all one temperature. At 1440 m it has not frozen since the 14th April.

The old snow layers (February crusts) could cause a concern as the snow pack above is loosing strength fast and large natural triggers such as cornices could take off all the snow we have had since March down 50 to 2.5 meters deep.

In the worse case: a Cornice Falls and triggers a large slope down into the March/April snow which then steps down to the February crusts. This could be up to 3 meters deep with the right trigger in the right terrain...

Consider using SIMPLE or CHALLENGING TERRAIN with lower angle 38 degree slopes and more supportive shapes and less wind loading exposure.  Avoid Solar aspects and gullies and drainage type features with rocky overhead terrain as 'garbage day' is expected.

Travel advisory:

Monday: Human Triggering is Possible to UN-Likely in the Alpine and improving for Tuesday and Wedensday as a slight cooling and drying  trend develops. 

Outlook:

Generally it will be too warm, with some overnight freezing depending on sky cover and elevation. Freezing levels between 1300m and 2500m with some surface refreezig expected. Monday AM fairly steady rain showers possible.  Winds Light going South through West as it dries into a 'Sunny' day for Wednesday.

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

Outlook	Monday	Tuesday	Wednesday
Alpine  1560 m 2200 m	CONSIDERABLE	MODERATE	MODERATE
Treeline	MODERATE	MODERATE	MODERATE
Below Treeline	LOW	LOW	LOW

Confidence: Good. Freezing levels and day time temperatures will be the chief thing to watch.

 Main Concerns:

• Wind Slabs and fresh redeposited Wind Slabs, isolated in Alpine & Tree Line East, North, North West
• Cornice Fall  (natural trigger)
• Solar or Steep slopes, wet surface slides (natural trigger) 

Weather:

Since Friday The Island Alps received flurries sunny breaks giving another 10 to 20 cm snow and some clear breaks with above freezing temperatures and then cool temps in the eves and winds that were moderate at ridge top from the South East, South and West.

The outlook the start week is mostly clear with possible PM flurries into Wed, should be all cold nights and day time freezing levels rising a little higher each day to 1750m on the South and East Island 1500 m North Isle.  Light to Moderate winds starting from East and South and moving through the week to West and then North or North West by Wed.

Avalanche Activity:

Thaw cycle activity is occurring. Steep ground natural slough triggered size 2 slab in alluvial fan. Suspect some cornice falls and resulting wind slab triggered as well as point release wet and dry.

Snowpack:

At lower elevations a Melt freeze crust is faceting over night and gaining surface hoar. North and cold slopes in the Alpine are still soft but gaining a temperature crust below 1500m.  Solar aspects are consolidating fast and steeper terrain is shedding and pin wheeling. Most of last weeks' snow is somewhat up side down due to temperature and or wind. Expect surface hoar development.

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  moderate to hard  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 38 degree slopes and more supportive shapes and less wind loading exposure.  Avoid Solar aspects and gullies and drainage type features with rocky overhead terrain as 'garbage day' is expected.

Travel advisory:

Monday: Human Triggering is Probable to Possible in the Alpine and improving for Tuesday except Solar aspects. 

  Monday, Tuesday and Wednesday Natural Triggering is Probable as Loose snow instabilities and cornices may fail 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 Cornice formation exists NW through East and is very acutely 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 Possible to Unlikely.

Outlook:

Spring mixes with winter\: Clear cool nights with days that will be too warm, isloated PM showers possible. Winds Light going South through West and into North as ridge of high pressure sits over us for the mid week.

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. 

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

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

Confidence: Good

 Main Concerns:

• 48 hour Storm snow (35 TO 55 CM)
• Wind slabs at and above Tree Line
• Fresh Cornice development

Weather:

Friday and Saturday saw freezing nights and just over freezing days with a few flurries or wet snow showers, except the west Isle area which saw 20 - 30mm  rain/snow with + temps.  Saturday night The Island Alps received a blast of winter. 15 to 25 cm snow with high winds and Freezing Levels at or around 1100 m. Flurries continued Sunday and by Sunday night the next system hit the Coast bringing more snow and high winds. Storm snow by Monday 40 to 60 cm.

The outlook is for lighter snow Tuesday 15 cm to 50 cm. By Wednesday the snow lets off to 5 cm or less it cools to 600m or lower.  Winds Lighter W SW except during snow showers,  and lighter again Wednesday WNW.

Avalanche Activity:

SC size 1.5 crossloaded wind slab 10 to 25 cm deep 40 degree convex roll facing West. ran into trees. AC produced out of steeper ground a few small size 2 s and cornice pieces. Lots of skier slope use on steep ground in new snow with no sluffing to speak of.

Snowpack:

New storm snow (55 cm ) and wind slabs are bonding pretty well over the older snow and crusts. A layer of plates is producing shears above the crusts in some places.  Below our current late March snow the Mid March snow and old wind slabs sit on older crusts down 30 to 120cm down. Most of these layers melted and refroze together during rain events consolidating the upper pack. At higher elevations some of the poor bonds in the Old crust mid March snow are worth thinking about, especially in the thinner scoured and cross loaded Easterly or SW aspects where weak crusts with facets may still linger.

 

Terrain Advisory:    Travel in COMPLEX  avalanche terrain is not recommended. Travel below large overhanging cornices and on or under very steep loaded slopes is not advised. 

Travel advisory:

Human Triggering is Probable to Possible. Isolated 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 Cornice growth is still tender for the time being. The thinner crossloaded features were more sensitive to human triggering today than the deeply loaded lee aspects.

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

Outlook:

The outlook is for Winter to finish off March.  Snow 25 to 45 cm into Monday and into Tuesday 15cm  (to 25 cm more if you are on the North Island), tapering off (maybe) for Wednesday 5 or less. It remains cool and mostly clear with FL dropping from 1000m to 600m. Winds ease Monday PM to West and back to S SW Light with a few gusts for Tuesday's system and lighter again from WNW Wednesday.