Saturday January 4, 2020
Cornice Fall, Wet Slab, Loose Wet, Deep Persistent Slab, Storm Slab
Travel & Terrain Advice
Natural Avalanches possible. Human triggered avalanches likely. Stick to lower angled terrain. New snow varies in terms of deposition and volume across Vancouver Island. Be aware as you move through the terrain for shooting cracks and signs of instability (including new avalanches). Convex unsupported terrain features in leeward (down wind) terrain would be an area to be highly cautious of when navigating through the backcountry this weekend.
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.
Friday’s overnight Rain into the early hours of Saturday will hasten potential for cornice fall. Extreme winds and up to 50cm of additional snow on Saturday will increase the probability for cornice failure due to High winds and new snow.
Monday’s forecast of snow and rain will also exacerbate stability and further stress the snowpack. New snow and rain fall Monday could create dense moisture laden upper snowpack primed for triggering.
On Monday, rain is forecasted at treeline and Below Treeline elevation bands, further aggravating the recent storm snow interface from earlier in the weekend.
Deep Persistent Slab
A surface Hoar layer that has been reactive to testing in the field will become a potential major hazard (at Treeline and Alpine elevation bands) for larger scale avalanches (size 2.5) as the Surface Hoar persists it will undergo a major loading event from the forecasted rain and snow in the next 48 HRS. This Surface Hoar layer has been found on all aspects at Treeline and Alpine elevation bands and in areas where surface hoar has grown while protected from winds. This layer of surface hoar has been very stubborn to initiate however it would be wise to be extremely cautious as there is substantial new “load” acting on the snowpack as a result of rain, storm snow and extreme winds.
Major precipitation in the form of snow and wind will cause major instabilities in the snowpack. Expect all Alpine and Treeline environments to be very likely areas to trigger an avalanche.
The snowpack was generally well settled with very little information regarding avalanches having occurred recently on the island. The major warming trend, coupled with 50+mm of rain and up to another 50+cm of new storm snow will arrive over the next 24 HRS. As a result, we could expect major snowpack volatility and instability over the course of the weekend.
|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|
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.
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 to minus 7 degrees, 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
Posted on Saturday January 4, 2020 by Ryan Shelly