Regions
Vancouver Island.
No new significant avalanche observations have been reported in the past three days. Mt Washington patrol saw some small size 1 Loose dry and Loose wet sloughs on Thursday, as the 2 cm of new snow slide easily on the old surfaces it landed on. Within the past week a group of skiers (near Mt Washington) triggered a size 1.5 avalanche on a north facing, treeline, wind loaded, convex roll that has produced many avalanches (both human and naturally triggered) in the past (ie a regular producer of avalanches over the years). This slid on the persistent weak layer above an old crust approx 20 -30 cm deep (as of Thursday). Some equipment was lost but no injuries were reported.
Past Weather
2 to 10 mm of precip has fallen in the mountains since the last bulletin. This new precip has fallen as a mix of rain and snow at all but the high alpine zones (were it was all new snow). Temperatures have ranged from -3 to +3 leaving a warm upper snowpack.
Weather Forecast
A significant snow event is forecast for Friday. Early Friday rain will change to snow and strong winds are expected from the SW to SE. Things will ease off Saturday into Sunday. Friday - 3 to 10 mm of rain changing into snow with 10 to 30 cm of snow accumulating. Winds strong SW to SE. Temps +1 dropping to -4. Freezing level 1700 dropping to 1000 m. Saturday - a trace to 4 cm of new snow. Winds Moderate NW. Temps cold at -4 to -7. Freezing level 400 to 900 m. Sunday - 1-3 cm of new snow. Winds light W to SW. Temps -4 to -7. Freezing level 0 to 800 m.
Terrain Advice
Significant new snow will fall on Friday with strong winds from the SW to SE. Avoid wind loaded features in the alpine and treeline until this snow has had time to bond to the old snow. Travel in avalanche terrain is not recommended when the avalanche danger is at high. A persistent weak layer in the upper snowpack has the potential to make small avalanches grow (step down) into larger ones. It would be smart to avoid big terrain features this weekend, even though the new snow is tempting you.
Snowpack Summary
We currently have a weak layer lingering in our upper snowpack and we have seen recent avalanches triggered by skiers on this weakness.
Snowpack Details
- Surface: Wet snow from rain and warm temps Thursday at all elevations except the high alpine.
- Upper: 20-50 cm of snow from previous storms with a few thin crust layers
- Mid: Down 20 to 50 cm is an old crust that has weak snow crystals on top of it (weakness over an easy sliding surface)
- Lower: Well settled
Confidence
High - Weather models in agreement and good field data.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.