Avalanche Forecast

Fair - Intensity of incoming weather is uncertain on Tuesday

A trough of low pressure anchored over SW BC allows for moist SW flow for the forecast period. Snowfall picks up again around 10 pm Sunday night & with the South Columbia's picking up the bulk of the storms energy, 10 - 20 cm are expected overnight. MONDAY: Monday morning should be cool & crisp with freezing levels at valley bottom, but the cold won't last long, freezing levels climb to 1500 m before lunch as snow fall begins. 5 - 10 cm's are expected during the day with strong SW winds at ridge top & a more moderate southerly at treeline. Remnants of a deep pacific low slide through the region Monday afternoon/evening bringing ridge top winds up to extreme. 5 - 10 cm of snow are expected Monday evening. TUESDAY: SW winds in excess of 100 km/h at ridge top persist through most of Tuesday. Another 5 - 10 cm are expected Tuesday with intensities tapering Tuesday afternoon. SW winds in excess of 100 km/h at ridge top persist through most of Tuesday. WEDNESDAY: A brief ridge of high pressure is in place Wednesday morning, but, the current models show another significant system moving into the region Wednesday afternoon.

Low level cloud made for poor visibility Saturday, as a result, there isn't much to report in the way of avalanche activity. Sluggish sluffing in the storm snow was observed in steep terrain on Saturday though. I've left a few observations from the last 72 hours in place as they help to illustrate how tricky and destructive the Persistent Slab problem is. 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 Saturday, bringing the weekend storm total to 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.