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Avalanche Forecast

Archived

Dec 23rd, 2020–Dec 24th, 2020

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Vancouver Island.

Mt Washington Patrol reported a few avalanches with ski cutting control work up to size 1 loosed dry sloughs on Monday and no new activity on Tuesday. No other reports of avalanche activity were reported. We would like to remind folks to send in their snow, avalanche and weather info directly to this bulletin. Please send your snow stories to [email protected] as your info greatly helps us write more accurate bulletins for everyone's safety. It does not have to be technical snow terms... just write in your own words what you saw and how it all went out there. The great news is that, if you report to us directly, you will often get contacted by our on duty forecaster to discuss your info so its a great two way learning experience.

Past Weather

Monday saw an average of 10 -15 cm of new snow fall for all but the northern hills. Strong to extreme winds redistributed this snow from NW slopes to SE (atypical for the island). Tuesday was a mainly sunny with cold temperatures and light to moderate winds still from the NW.

Weather Forecast

Little to no new snow for Wednesday and Thursday with temperatures unfortunately rising into the positive numbers. Mainly cloudy with light to moderate winds Wednesday, increasing to moderate to strong Thursday from the south. The next blast of precipitation comes in warm on Christmas day (warm is how we like our Christmas dinner but not our storms). With varying precip amounts and varying in what form it will fall in, from 10 to 40 mm of rain or if that's all snow 10 to 40 cm of snow. Wednesday: 0 to a trace of new snow, light to moderate winds from the S to SE, temps for 1500 m -3 to +3, freezing level sea level to 700 m. Thursday: 0 cm of new snow, moderate rising to strong S to SE winds, temps for 1500 m +4 dropping to -1, freezing levels as high as 2500 m. Friday: 10 to 40 mm/cm of precip (mm if rain cm if snow), winds strong to extreme from the S to SE, temps for 1500 m +1 to -1, freezing levels 1800 to 900 m.

Terrain Advice

Watch out as temperature will rise Wednesday and Thursday. The jump in warmth has the potential to create loose wet avalanches and may also make the weak layers in our current snowpack more sensitive to triggering (likely to slide). Avoid steep solar slopes during warm times and avoid exposure above terrain traps, which these wet slides can push one into (creeks, gullies, bands of trees, cliffs). Terrain traps can increase the depth of burial and/or chance of injury. A warm storm is headed our way on Christmas day. The type of precipitation that will fall may vary based on temps at elevation. It may be rain, mixed rain and snow or all snow. Forecast weather models vary on what elevation the snowline will sit at for different locations on the island, so keep an eye on this when choosing were you will go to play. The south island appears to be warmer up high than the north so there is a greater chance of rain in the hills down there vs snow.

Snowpack Summary

An average of 10 to 15 cm of new snow fell on Monday with only the north island (Mt Cain) reporting less (2 cm). The new snow came with very strong winds from the NW that really affected the snow surface conditions. Surface conditions vary from light low density powder in very wind sheltered pockets, to very bumpy wind slab features, to zones where all the new snow has been stripped off down to the old rain crust from days back.

Snowpack Details

  • Surface: Wind ravaged with features that look like something out of a science fiction novel. lol
  • Upper: 10-15 cm of new snow mainly wind pressed where it came to rest over a thin decaying rain crust
  • Mid: 10-20 cm of old snow over another beefier rain crust capping another 20-50 cm of well settled snow
  • Lower: An old crust (showing signs of decay) over well settled snow.

Confidence

High - Weather models in agreement and good field data.

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.

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.