Regions
Vancouver Island.
Multiple reports of size 1 and size 2 skier triggered avalanches throughout the forecast area. These avalanches have been reported as 'slab' avalanches, they will remain sensitive to skier/snowmobile triggering as the reports include shooting cracks.
Past Weather
The past week saw cool clear calm temperatures allowing for the growth of two separate (PWL's) within the upper snowpack. A storm cycle on Sunday brought close to a foot of new snow to various parts of the forecast region and along with it a variable deposition of the new snow as winds in certain regions redistributed new snow to downwind areas.
Weather Forecast
On Monday, a weak low pressure system with periods of snow over the island. The highest accumulation of precipitation will likely occur from the central portion of the island and to the South. This low is expected to dissipate by Monday night. As the storm subsides, cold air from the interior will move to the coast which will be accompanied by strong outflow winds developing on Tuesday and into Wednesday. Monday: 10cm to 30cm Snow, High - 3 Low -5, Light Winds from the NW, Freezing level 550MTuesday: 5cm to 10 cm Snow, High -1 Low -4, Moderate to Strong winds from the East, Freezing level 500M Wednesday: 2cm to 5cm Snow, High -3 Low -8, Freezing level 400M
Terrain Advice
The recent storm snow has formed slabs in specific downwind areas that are reactive to human triggering. Be aware of the potential for loose dry snow avalanches in steel unsupported terrain. On Tuesday, with the continuation of the storm and potential wind, cross loaded and down wind areas will remain a concern to prioritize if venturing into avalanche terrain. Be conservative when travelling nearby to cornices as they are generally unstable (very much so at this time during a storm/wind cycle). Maintain a close eye on the transition areas between wind scoured and snow loaded areas as these zones can be good areas to initiate avalanches at this time.
Snowpack Summary
10-30cm of wind affected new snow overlies an array of supportive melt freeze and rain crusts within the upper 50cm to 70cm of the upper snowpack. The crust at the Below Treeline elevation band is extremely supportive and providing difficult snowmobile and ski conditions in wind exposed areas where the new snow is no longer present.
Snowpack Details
- Surface: 10cm to 30cm of new snow overlies surface hoar (PWL) in specific areas (wind sheltered terrain)
- Upper: 40cm below the surface exists a melt freeze crust with facets (PWL) resting above this crust
- Mid: generally well settled with several melt freeze crust layers
- Lower: well settled and well bridged and includes a 10cm thick layer of large facets
Confidence
High - Weather models in agreement, a great deal of professional and recreational observations. This weeks report brought to you in collaboration with shadow forecaster Dave Kallai and Forecaster Ryan Shelly
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.
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.
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.