North Columbia Avalanche Forecast Date/Time issued: Friday, March 20, 2009 at 4:00 PM Valid until: Monday, March 23, 2009 at 6:00 PM Next Scheduled Update: Monday, March 23, 2009 ---------- Cariboos ---------- Saturday Sunday Monday Alpine 4 - HIGH 3 - CONSIDERABLE 3 - CONSIDERABLE Treeline 3 - CONSIDERABLE 3 - CONSIDERABLE 3 - CONSIDERABLE Below Treeline 3 - CONSIDERABLE 3 - CONSIDERABLE 2 - MODERATE Confidence: Fair. If snowfall amounts are as expected we should see HIGH avalanche danger in the alpine and possibly at treeline on Saturday. Primary Concerns: * Persistent Slab: Several persistent weak layers (PWLs) in the upper snowpack are primed for natural and human triggered avalanches this weekend. Basal weak layers of facets and depth hoar are beginning to wake up on re-loaded bed surfaces or in specific terrain and are resulting in very large and destructive avalanches. * Solar Radiation: Intense spring sunshine could trigger large natural avalanches on sun-drenched slopes. * Cornice: Recently formed cornices may fail under mild conditions and periods of intense sunshine. Special Message: A Special Public Avalanche Warning has been issued for most of south and central British Columbia including the North Columbia Mountains. Travel Advisory Issued: Fri, Mar 20 Next Scheduled Update: Mon, Mar 23 Backcountry travel is not recommended in anything but simple terrain this weekend. Conditions are very touchy and the possibility of triggering very large and destructive avalanches is high. I recommend sticking to the trails or low-angle glades and meadows. It may be possible for large avalanches to run to valley bottom, especially on large south-facing slopes, so make sure you are well away from avalanche paths and runouts. Don't let the sunshine and blue skies tempt you into skiing riding bigger slopes. It's definitely not a good time for riding aggressive lines or climbing and highmarking. Conservative decisions are highly recommended this weekend! Avalanche Activity Issued: Fri, Mar 20 Next Scheduled Update: Mon, Mar 23 It is likely that a widespread natural avalanche cycle continued on Friday with mild temperatures, continued incremental loading, and rain at lower elevations. Numerous natural avalanches up to size-3 were reported on Thursday on all aspects, but observations were still limited due to poor visibility. Human-triggered avalanches are likely this weekend. It may be possible to trigger very large, high consequence avalanches on all aspects and at all elevations. Click here to read about a recent fatal avalanche near Mica Mountain in the Cariboos. Snowpack Issued: Fri, Mar 20 Next Scheduled Update: Mon, Mar 23 80-120cm of snow has fallen in the past week. This is a substantial amount of load in a very short time! The new snow has fallen under generally mild conditions and moderate or strong southerly winds. This has resulted in the formation of a deep soft slab overlying a variety of PWLs and dense wind slabs on NW through E facing slopes. There are several easy or moderate shears within the storm snow, but more significant are consistent moderate "pops' shears on the early March suncrust or facet layer down 80-120cm. Deeper PWLs like the late Feb. surface hoar/crust combo or the basal facets and depth hoar remain a concern. There is potential for smaller avalanches to step down to these layers and produce very large, high consequence avalanches. Weather Issued: Fri, Mar 20 Next Scheduled Update: Mon, Mar 23 An additional 10-20cm of snow is possible by Saturday morning before a building upper ridge of high pressure results in partial clearing overnight and through the weekend. Winds should be gusting to moderate or strong from the southwest. Saturday, Sunday and Monday should see a mix of sun and cloud. The freezing level should be around 1000m on Saturday and near valley bottom on Sunday and Monday. Winds should be light and variable through the weekend. The next system is forecast to reach the region by Monday night bringing moderate snow. Issued by: Peter Marshall