Regions
Vancouver Island.
Mt Washington patrol avalanche control Thursday: couple naturally triggered wind slabs to size 2 N aspects treeline down 30-40 cm, few ski cut size 1.5 on N to E aspects treeline down 10-20 cm, and many ski cut size 1 avalanches both wind slab and loosed dry on W-N-E aspects treeline and below treeline down 10-15 cm. All running down on the old crust layer.
Past Weather
The new snow that fell Wednesday night into Thursday morning was redistributed by strong to extreme winds from the S-W.
Weather Forecast
The strong to extreme winds continue, transitioning from south and west to northwest overnight Thursday and though the day Friday. Some new snow will fall with the biggest accumulations for northern areas. Sunday sees temps climb as the freezing levels goes to near 1500 m island wide. Friday: 1 to 15 cm (largest amounts for the north island), winds strong to extreme NW, temps for 1500 m -4 to -8, freezing levels 400 to 950 m. Saturday: no new snow to a trace of new, winds moderate to light NW to SW, temps for 1500 m -3 to -9, freezing levels 0 to 800 mSunday: 5 to 10 cm (with some rain or a rain snow mix for low elevations), winds strong to moderate S to SW, temps for 1500 m 0 to -5, freezing levels 600 to 1500 m.
Terrain Advice
Avoid wind loaded zones/pockets on the lee side of ridges, in bowls, and on cross loaded features. Give these new windslabs time to heal and bond to the slippery sliding surface (the crust) they have landed on. Keep an eye on the temperatures Sunday as freezing levels rise, especially at below treeline elevations. Watch for hints like trees shedding their snow, and pinwheeling. Solar aspects may be the most prone to loose wet avalanche activity. Avoid exposure to cornices, both from above and below, as they will certainly have grown with the latest winds. The warming Sunday might also make them more sensitive to failure.
Snowpack Summary
New snow fell Wednesday night into early Thursday morning with anywhere from 6-30 cm. 6-10 for the east and southern zones, around 15-20 for the west and Strathcona, 20-30 for the north. Extreme winds stripped this new snow off windwards to the old crust and built significant windslabs on lees loading the crust. The mid and lower snowpack is well settled.
Snowpack Details
- Surface: Wind affected surfaces in all but the most well sheltered pockets (where new snow remains preserved)
- Upper: A crust with variable support to skis and unsupportive to sleds and foot traffic. Some dry loose snow under.
- Mid: Well settled with a dormant persistent weak layer and old crusts
- Lower: Well settled
Confidence
Moderate - Widespread extreme wind event island wide so significant new snow being transported to lees, very few public reports, warm up forecast for Sunday but that's three days way at time of writing (Thursday night).
Problems
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.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.