Purcells

Fair - Intensity of incoming weather is uncertain on Monday

Saturday Night: I expect very light snowfall at and above treeline Saturday night with freezing levels dropping down to about 1000 m by Sunday morning. Overnight snow totals look to be between 5 & 10cm. Ridge top winds should be strong at overnight, with moderate winds at treeline. Sunday: Freezing levels creep back up to around 1000m for most of the day, dropping to the surface with the passage of the cold front Sunday night. I expect 5 - 10 cm of snow during the day Sunday above 1200m. Winds remain strong & steady out of the SW at ridge top. Monday morning offers respite from the precip and warmth. Freezing levels creep up to 1200 after lunch Monday as snow begins to fall, starting lightly, increasing in intensity overnight. I expect 10 - 20 cm of new snow by the time skies clear Tuesday evening.

We didn't receive much in the way of avalanche observations Saturday as visibility was limited in the region. The following observations are from Thursday/Friday: In the dogtooth backcountry, observers reported a size 2.5 avalanche with a crown 1m+ in depth, that was likely human triggered. Explosive control work once again produced large avalanches to size 3.5 on all aspects with crowns ranging from 40 - 120 in depth.

10 cm of moist snow fell Friday night continuing through the day Saturday accompanied by light to moderate SW winds. Freezing levels topped out around 1400m Saturday, with the top 10 cm moistening as a result. 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 90 - 160cm 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 90 -160 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. Basal facets have only been reactive on steep, shallow, and rocky slopes, but operators continue to monitor this layer in tests. Triggering this deep persistent weak layer is unlikely, but shallow snowpack areas or shallow weak areas adjacent to deeper wind loaded slopes are the most suspect locations.