Regions
Vancouver Island.
Limited field observations, however we are expecting major storm snow and extreme winds over the weekend. Watch for precipitation amounts and storm snow loading in excess of 30cm and monitor wind speeds as snow transport and redistribution will be very important in determining where avalanches will occur. Natural avalanches are likely this weekend at Alpine and Treeline elevation bands if the forecasted wind speeds and snow volume arrives.
Past Weather
Several moderate snowfall events earlier in the week have bonded due to warm winter air temperatures and rain (including rain in Alpine) which has helped facilitate bonding.
Weather Forecast
A large storm cycle of extreme precipitation, wind and freezing level fluctuations is expected over the next 48 HRS. Saturday - warm temps from Friday will subside and rain will transition to snow (10cm-60cm), Extreme Winds will relocate snow to Easterly Aspects, Temps O degrees - minus 7, Freezing Level 700M Sunday - Another 20cm - 50 cm of snow is expected, Extreme Winds will lessen throughout the day but expect more snow transport to multiple aspects as wind direction varies widely during the storm cycle on Sunday, Temps -1 to -7 degrees, Freezing Level 800M dropping to 400M later in the day. Monday - More "Classic West Coast Weather" - Forecast models approximate between 10cm -15 cm of snow and later in the day a transition to 10mm - 30mm of rain as the air temperature goes from minus 6 degrees to +2 at 1500M of elevation
Terrain Advice
Very dangerous avalanche conditions. Travel in avalanche terrain is not recommended at Alpine and Treeline Elevation bands.
Snowpack Summary
The snowpack was generally well settled will very little information regarding avalanches occurring. The major warming trend, coupled with 50+mm of rain and up to another 50+cm of new storm snow over the next 24 HRS we could expect major volatility within the snowpack.
Snowpack Details
- Surface: 50+ MM of Rain and another 50MM of snow is forecast in the next 24-36 HRS leaving the upper snowpack and Storm Snow highly unstable
- Upper: Generally well settled however new rain and major warming events may lessen consolidation, particularly on storm snow interfaces from earlier in the week and overnight into the weekend
- Mid: Well bonded midpack that does include two weaker layers (Facet layer and Surface Hoar layer)
- Lower: Well Settled except on exposed rocky cliffs and rocky outcroppings where basal facets are lingering in Alpine
Confidence
Moderate - Weather models in agreement, moderate field weather and snowpack observations, limited weather station data
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.
Wet Slabs
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
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.
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.