Monday December 14, 2020
Loose Wet, Wind Slab, Storm Slab
Travel & Terrain Advice
Careful route finding and snow-pack evaluation are paramount during periods of sustained moderate to strong snowfall this week as well as a fluctuating air temperature (Critical Warming) and strong winds.
Avoid traveling both above and below cornice features.
Careful and cautious route finding when entering into or over convex rolls or steep features.
Human Triggered avalanches are “likely” to be initiated by skiers/snowmobilers/snowshoers on Tuesday and Wednesday if forecasted precipitation and winds arrive as scheduled. Finding lower angled terrain (generally less than 30 degrees) should be considered an appropriate choice given the increasing avalanche risk on Tuesday and Wednesday.
No new avalanches reported either via email to Forecaster@avalanchebulletin.com nor have there been any reports via Mountain Information Network via Avalanche Canada App
Some reports of people pursuing some larger ski objectives/descents on the weekend (thank you Mike Hudson and Markus Rannala for sharing your info/beta!) No avalanches reported and good boot top powder conditions were noted in multiple areas above 1300M of elevation.
Moderate Rain events at lower elevation. On Tuesday Rain up to 1300M of elevation could exacerbate new storm snow instabilities with additional rain loading of fresh snow. In addition to Rain and snow events especially Tuesday into Wednesday, the increased daytime warming coupled with rain on surface snow may cause snow to become unconsolidated.. This avalanche problem when triggered is likely to remain small, but on isolated terrain features that are steep, these features will promote a small avalanche to gain mass and result in a large, size 2. Expect this avalanche problem to become more prevalent once the incoming rain arrives in addition to rising air temperature (particularly Tuesday).
Location: On all aspects and found at Below Treeline and possibly up to the Treeline elevation band on Tuesday and possibly Wednesday depending on actual volume of rainfall received.
Possibility: Triggering of this avalanche problem is possible from light loads such as skiers. Natural avalanches are unlikely.
Size: If triggered expect these avalanches to be small, and on isolated terrain features large, size 2.
Moderate to Strong precipitation in the form of storm snow coupled with strong winds on Tuesday into Wednesday could promote wind slab instabilities (particularly in leeward or down wind areas) on Vancouver Island. Expect all Alpine/Treeline environments in leeward/down wind terrain to be likely areas to trigger a wind slab avalanche on Tuesday and Wednesday.
Location: Leeward and down wind aspects at Alpine and Treeline elevation bands.
Possibility: Triggering of this avalanche problem is likely (depending on Elevation) from light loads such as skiers or sledders. Natural avalanches are unlikely to likely (depending on Elevation).
Size: If triggered expect these avalanches to be up to size 2 OR avalanches could appear on isolated terrain features (very large, size 3).
New snow from incoming storm system will rapidly fall on a variety of surfaces. Expect this new avalanche problem to be initially very touchy to light triggers such as skiers or sledders, particularly on Tuesday and on Wednesday when snowfall amounts increase substantially.
Location: All aspects and at all elevations. New Storm snow may fall as rain at the Below Treeline Elevation Band on Tuesday and Wednesday.
Possibility: Triggering of this avalanche problem is likely to unlikely (depending on Elevation) from light loads such as skiers. Natural avalanches are possible to likely.
Size: If triggered expect these avalanches to be small (Size 1) -and large (up to size 2) OR avalanches could appear on isolated terrain features (very large, size 3).
Limited observations at this time however snowpack depth decreases substantially lower than the 1200M elevation band. Recent snowpack summaries show a depth of 90cm of Snow at an elevation of 1400M in the Mount Washington area.
Several melt freeze crust have developed on all aspects at the Treeline and Alpine elevation bands on Vancouver Island. The upper snowpack melt freeze layer is not yet completely frozen (in certain areas) and reports show that this layer is still isothermal (0 degrees) and slushy (in certain areas). In zones where freezing temperatures have remained consistent, the upper snowpack melt freeze crust is frozen completely, a facet layer is developing and is showing results on testing at this upper snowpack melt freeze crust interface. However no reports of skier/snowmobile triggered avalanches at this time.
|Surface||10-15 cm thick wind slab (Monday Dec 14) exists in specific downwind terrain. Also 10-20 cm of fresh boot top powder snow exists in wind protected area that are at treeline/Alpine elevation|
|Upper||A melt freeze crust and facet interface showing results to testing in Mount Washington area|
|Mid||Well settled due to melt freeze cycle snowpack has undergone|
|Lower||Well settled due to melt freeze cycle snowpack has undergone|
Weather has been cool (below zero) in the mountains of Vancouver Island for the past week. This cooling trend has helped consolidate snow that had previously been exposed to above zero temperatures. General weather pattern this past week helped to consolidate snowpack.
Substantial precipitation and strong winds incoming over the next few days. This will include increased precipitation and varying snow/rain on Tuesday (this dynamic weather) is responsible for increasing avalanche hazard. Alpine and Treeline elevation bands will prevail in terms of gaining the most amount of new snow without rainfall. Strong sustained winds however will also prevail during Tuesdays’s storm event.
Posted on Monday December 14, 2020 by Ryan Shelly