Regions
Vancouver Island.
Confidence
High - Weather models in agreement and good field data
Travel & Terrain Advice
Travel in avalanche terrain is not recommended when the avalanche hazard is posted as high. Significant quantities of dense new snow are forecast to fall on a widespread weak layer from last weekend (surface hoar). Give avalanche paths and their runouts a wide berth as they have the potential to run further than one may expect during this forecast period even into paths that stretch down into lower elevation bands. Cornices will be additionally loaded and travel above and below then should be avoided. Dense low angled forests would be the place to be if you are heading out to play.
Avalanche Summary
Friday - Mt Washington avalanche control produced numerous soft slab avalanches up to size 1.5 on N-NE asp at treeline and below. Sunday - Ski cutting was still producing easy loose dry avalanches on steep N treeline terrain down approx 10 cm.
Snowpack Summary
Cold new snow fell Friday. The weekend saw small amounts of new snow with some isolated convective activity producing some graupel. The big story was widespread surface hoar that developed over Saturday night and remained intact at the end of Sunday on all aspects at treeline and below. Early Monday morning the next snow fall began over the entire forecast region, with greater quantities falling to the north (Mt Cain region).
Snowpack Details
Surface: New snow over a suspected weak layer (surface hoar). Upper: Recent storm snow from last week, bonding moderate to the March 22 crust. Mid: Well settled. Lower: Well settled.
Past Weather
Nice new snow for folks fell Friday. The Weekend was a mixed bag of conditions with a little bit of new snow, large temperature fluctuations between day and night (-8 to +3 at times) and even a little convective activity and graupel. Winds were general light to moderate form the SW.
Weather Forecast
Significant new snow fall (potential mixed precip at lower elevations) with warm temperatures and strong SW winds Monday into Tuesday. Monday: 9 to 40 mm of new precip, winds moderate rising to strong SW, temps -3 to +2, freezing level 1200 rising to 2300 m overnight. Tuesday: 6 to 17mm of new precip, winds strong SW dropping to L W, temps +2 dropping to -3, freezing level 2300 dropping to 1000m. Wednesday: trace to new new precip, winds light to moderate N-W, temps -1 to -6, freezing level 700 to 1000 m.
Problems
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.