Avalanche Forecast

Fair - Due to variable snowpack conditions

Heavy snowfall is expected overnight (Monday night), especially for the southern part of the region with 25-30 cm possible in some areas by morning. Areas to the north will likely see less snow. Strong to extreme SW winds, freezing levels around 1100 m. On Tuesday, heavy snowfall will continue into Tuesday morning but become lighter in the afternoon. Winds should also start to diminish. Freezing levels should fall slightly. On Wednesday, there may be a lull between storms, although snowfall is expected to start up again later on in the day. On Thursday, another frontal system arrives in this region, bringing further heavy snowfall, strong SW winds and freezing levels in the 1200 m range.

On Sunday a fatal avalanche incident south of Revelstoke occurred. The initial police report is here: http://revelstoke.rcmp.ca/ViewPage.action?siteNodeId=503&languageId=1&contentId=24477. We'll try to post more details as they become available. Other human-triggered avalanches were reported up to size 2 and natural avalanches were reported up to size 3 on a variety of aspects and elevations. This activity builds on a very active period of avalanche activity from the last week. Some events that illustrate the ongoing severe nature of the avalanche problem are included here: From Friday: In the greater Revelstoke area two size 2.5 naturally triggered avalanches were observed on a West facing slope. Just north of the forecast region a skier remote triggered a size 2.5 avalanche from 20m away on a low angle cross loaded slope just below tree line. From Thursday: Explosive control work produced spectacular results with avalanches to size 4 on all aspects. Crowns varied in depth from 100 - 200cm. Numerous natural avalanches were reported from size 1 - 3. I found the following report particularly noteworthy: A chunk of cornice fell from ridge top initially triggering a size 2 avalanche. The avalanche ran 50m as a size 2 before stepping down & triggering a size 3 avalanche in lower angle terrain. The crown was reported to be 200 cm in depth, failing on the Feb. 08 surface hoar.

Another 10 cm of moist snow fell Sunday night, adding to storm snow amounts from the weekend of 20 - 30 cm, most of which has been accompanied by moderate SW winds. This new snow covers old pencil hard wind slabs which were created by last week's strong W/SW winds. These wind slabs are getting more stubborn, and it likely takes a big trigger, like a falling piece of cornice to get them going. That being said, they may still be sensitive to human triggering in areas where the snowpack goes from thick to thin, rock outcroppings being the classic example of this kind of structure. The big story remains the early February Surface Hoar that is 80 - 170cm deep. The snow above this weak layer has been under the influence of warmth and time which has settled the snow into a thick cohesive slab 80 -170 cm in depth. Obviously, when a slab almost as tall as the average Canadian releases, the consequences are severe. Operators in the region have been diligently gathering data on this weak layer; In snowpack tests, the layer fails in a sudden planar fashion indicating that it has lots of energy in it, and showing that when it does fail, it has the potential to propagate across large distances. These tests mesh with the large avalanches that have been observed in the region recently. Conditions have been favorable for cornice growth recently, as a result many ridge lines are sporting large cornices.