Regions
Vancouver Island.
No new reports from the public of avalanche involvements.
Mt Washington patrol no new avalanche activity observed.
Would expect a widespread natural avalanche cycle in the alpine/ treeline from last Sunday night in to Monday morning's rain/wet snow event but few observations done or reported. Thanks Joe for your reports of this cycle from the Mt Cain region of multiple avalanches up to size 1 to 2.5 and potentially even a size three.
Past Weather
Sunday night in to Monday morning saw a rain event that saturated the upper snow up to approx 1300 m, with wet snow falling at higher elevations. Cold temps Monday re froze surfaces prior to variable amounts of new snow falling on the firm/crust surface. Moderate to strong SW winds have moved the new snow in terrain at treeline and alpine elevations.
Weather Forecast
Winds will start to pick up Wednesday as they usher in a big snow event set to arrive Wednesday night into early Thursday morning. The storm will taper off slowly with continued snowfall rates (moderate to light) by late Friday. The new snow will be accompanied by strong to extreme winds ranging from SSW to NW. Temps will peak during the storm (-2) then taper down after to near -6 -7. Wednesday: no new snow, winds light SE to strong S to SE, temps for 1500 m -4 to -7, freezing level 0 to 800 m.Thursday: 11 to 40 cm of new snow starting to fall Wednesday evening (heaviest amounts for the west side and north island), winds strong to extreme S to W, temps for 1500 m -1.5 to -5, freezing level 1000 dropping to 650 m. Friday: 3 to 25 cm (heaviest amounts for the north island), winds extreme to strong NW, temps for 1500 m -4 to -8, freezing level 1000 to 400 m.
Terrain Advice
Avoid wind loaded lee avalanche slopes and cross loaded features for the next few days and give the storm snow time to settle and bond to the firm slippery surface it will land on. Stay out of ALL avalanche terrain for elevations rated HIGH during this forecast period. Large quantities of snow with high to extreme winds all landing on a firm sliding layer add up to huge avalanche potential.
Snowpack Summary
Light to moderate amounts of new snow has fallen since the rain/warm up event last Sunday night into Monday morning. While snow amounts for the Mt Washington zone have been minimal, Strathcona Park and Mt Cain have received around 20 cm. Strong to moderate SW winds have transported the new snow in the alpine and treeline elevation bands creating wind slabs on lees and cross loaded features. The new snow has landed on a crust/firm snow surface that formed after the rain/ warm up event from Sunday Monday. A well settled upper/mid snowpack has basically eliminated the concerns of the persistent weak layers (PWL) that resulted in so many human triggered avalanches a few weeks back. These PWLs are now down approx 100 to 130 cm and are well bridged/ sheltered from the snow above.
Snowpack Details
- Surface: A trace to 20 cm of new snow, wind blown at treeline and alpine elevation bands.
- Upper: Frim snow/crust with variable support to ski traffic, over some dry older snow
- Mid: Well settled snow over the old PWL layers
- Lower: Well settled
Confidence
High - Similar surface conditions island wide. Weather models in agreement. Moderate to large amounts of snow with very high winds.
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.