Avalanche Forecast

Fair - Timing, track, or intensity of incoming weather is uncertain on Sunday

Saturday Night: I expect continued light snowfall at and above treeline Saturday night with freezing levels dropping down to about 1200 m by Sunday morning. Ridge top winds should be strong at overnight, with very little wind at treeline. Sunday: Freezing levels stick around 1000m for most of the day, dropping to the surface with the passage of the cold front Sunday night. I expect 10 - 20 cm of snow during the day Sunday above 800m. Winds remain strong & steady out of the SW at ridge top. Monday morning offers respite from the precip and warmth. Freezing levels begin to creep up after lunch Monday in combination with a trace of expected snow. Winds creep up to extreme at ridgetop Monday afternoon, but I expect a gentle breeze at treeline. Snowfall continues overnight Monday, we're likely to see 6 - 12 cm of new snow above 600m by Tuesday morning.

Avalanche observations really calmed down Friday, which is partially the result of poor visibility. Nonetheless, there are a few interesting observations to report. 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.I've left Friday's avalanche observations below, as they illustrate the nature of the current persistent slab hazard:From Friday: 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.

10 - 20 cm of moist snow fell Friday night into Saturday morning under light to 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.