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 Banff, Yoho and Kootenay National ParksIssued:Sunday, March 2, 2008 16:00Valid Until:Monday, March 3, 2008 16:00Bulletin Area:This forecast covers the east and west sides of the Continental Divide from the Wapta Icefields area in the north to the Sunshine area in the south. It also includes the Main Range area from Lake Louise to Bow Summit.
Synopsis:The main concern in the snowpack right now is the developing slab, at treeline and above. Though there was no new snow today, Westerly winds continued transporting previous day's snow onto lee aspects, further developing this layer. This new slab is of particular concern on Northeasterly aspects, where it overlies a weak layer of surface hoar crystals, which are well preserved and upwards of 2cm long. Triggering this instability is most likely in the immediate lee, where the slab has stiffened to 1 finger resistance and is 50 to 70cm thick. We are finding easy compression test results in this weakness, with sudden collapse characteristics. Again today, there was a skier triggered avalanche on this aspect, involving this weakness, at a location called Quartz Ridge, just outside the Sunshine ski area.Outside of this aspect, the new snow is bonding well with the oldsnow interface and adding to the midpack strength of the snowpack. However, more snow and extended periods of warm weather is needed, before we'll see widespread bridging of the weak basal facets. Today, a fracture line profile was conducted on yesterday's rider triggered avalanche and the associated remote avalanche. The initial slide involved only the new slab, but the slide it remotely triggered failed at the October 25th rain crust. The 3 meter, pencil hard blocks that slid down hill were a stark reminder of the deeper, lingering instability. Backcountry users must continue to be increasingly cautious in steeper, unsupported terrain, as human triggered avalanches remain probable in these locations. Avalanche Activity:One skier accidental was reported from Quartz Ridge, just outside the Sunshine ski area. Though not confirmed yet, the 50cm deep slab likely failed in the buried surface hoar. The slide was approximately 100m wide and ran close to 200m on a 35 degree slope.No natural activity was observed today. Outlook:An approaching Pacific low will hit the forecast region sometime Monday evening. Westerly winds will build to critical loading values and remain there through to Tuesday night. Approximately 5 to 10cm of snow will fall during the storm. Come Tuesday this should result in limited natural activity on steep, lee aspects, as cornices fail and the new slab overloads the shear strength it has with the interface below.Travel Conditions:Northeasterly aspects benefitted the most from the storm snow that arrived a couple days ago. After the fracture line profile at Bow Summit today, boot top turns were enjoyed in the fluffy snow that fell and was transported into the site. Ski penetration to ground should be just a bad memory in most locations, as the midpack is proving supportive for uptracking in most location now. MG
FOR MORE DETAILS:Warden Office: (403) 762-1470 Emergency: 403 762 4506 24 Hours Recorded Message: 1-800-667-1105 Related Link: http://www.avalanche.ca/ Seasonal Archives |
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