Regions
Vancouver Island.
Several reports from the mountain snowmobile and backcountry ski community have reported human triggered avalanches size 1-2 on leeward/downwind terrain. The layer responsible for the triggering is a wind slab occurring primarily on convex rolls.
Past Weather
Past precipitation amounts topped out at 90 mm on the west side of the island with snowfall amounts nearing 45cm on the eastern side. The winds and air temps increased and have factored into a combination of wind slab and developing melt freeze snow surface at the Treeline and Below Treeline elevation bands.
Weather Forecast
Friday: 1-2mm Rain, Winds Moderate from the South increasing to Strong South mountain top winds in the afternoon, Freezing level will reach a high of 1200 meters.Saturday: 5mm Rain and up to 10cm Snow North Island (with majority of precipitation arriving before dawn, Winds Moderate from the NW shifting to Strong NW mountain top winds in afternoon, Freezing level will reach a high of 1150 meters.Sunday: No precipitation expected, Winds Light from the NW, Freezing level will reach a high of 1700 meters.
Terrain Advice
Be cognizant of snow conditions and utilize small slopes to test and investigate the recent storm /wind slab snow and its reactionary properties.Careful and cautious route finding when transitioning from scoured areas into areas of wind loaded snow.Avoid traveling below and above cornice features as they are large and touchy.Avoid open and steep slopes during periods of warming and rain; even small loose wet avalanches will have enough mass to push a mountain traveler into gullies and over cliffs.
Snowpack Summary
Over the past forecast period intermittent moderate to heavy snowfall and intense wind transport was observed. A storm system delivered significant quantities of snow up to 90mm of precipitation on the west side of the island with moderate to strong winds from the South West. Evidence of intense wind transport of snow to North aspects was observed in both the Alpine and Treeline.Overall snowpack depths have been measured from 200cm to 400cm.A variety of crusts exist in the upper snowpack. Numerous snowpack tests indicate that these crusts are now beginning to bond to the storm snow.The mid snowpack has an unreactive 20cm layer of facets that can be found down 120cm and deeper. This layer may be isolated to areas that are sheltered and at higher elevations above 1400 meters presents as a melt freeze crust/ poly grain layer.The lower snowpack is dense and very well settled as many reports from island backcountry users and numerous snow profiles have indicated.
Snowpack Details
- Surface: Wind affected snow scoured on exposed South aspects with deep loading on North aspects. Solar aspects becoming moist 1400 meters and below.
- Upper: Storm snow and wind slabs from past storms can be found over a crust below 1500 m and over old storm snow above 1500 m.
- Mid: A 20cm layer of facets can be found down 100cm plus.
- Lower: Well settled and dense.
Confidence
High - Weather models in agreement, sufficient field weather and snowpack observations
Problems
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.
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.
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.