Purcells

Poor - Timing, track, or intensity of incoming weather is uncertain for the entire period

There is a high degree of uncertainty with regard to the weather forecast right now. Two cold fronts will affect the region this weekend bringing lowering freezing levels and an uncertain amount of precipitation. The following is my best shot at a forecast for the region. You will notice that the ranges are wide to accommodate the uncertainty. Light precipitation begins to fall Friday afternoon continuing through Saturday morning. 5 - 15cm are expected. Freezing levels top out around 2000 meters Friday afternoon. Saturday: Snow tapers Saturday morning, then picks up again in the afternoon. 3 - 10 cm expected during the day. Freezing level holds steady near 1500m Saturday with winds out of the SW moderate to strong at ridgetop, light to moderate near treeline. Sunday: Snowfall picks up near lunch time Sunday and continues to fall in earnest until midnight. 10 - 20 cm expected out of this pulse. Freezing level starts near 1500m falling to 500m by Monday AM. Winds similar to Saturday. Very little precip is forecasted Monday & freezing levels remain near the valley bottom. Winds stay out of the SW, light to moderate at treeline, moderate to strong at ridge top.

In the dogtooth backcountry, observers reported a size 2.5 avalanche with a crown 1m+ in depth, that was likely human triggered. Remote triggering of avalanches continues to be reported from the region. Explosive control work once again produced large avalanches to size 3.5 on all aspects with crowns ranging from 40 - 120 in depth.I've left the previous narratives in from earlier this because they help to illustrate the nature of the current hazard. From Thursday: Lots of avalanche activity to report from the region. In the north Moderate to Strong NW winds at ridge top continued to load lee slopes resulting in a natural avalanche cycle to size 2.5 with crown depths 20 - 60cm in depth. Just south of Golden explosive control work produced spectacular results with avalanches to size 3.5 & crown depths 100 - 160cm in depth. All aspects at & above treeline were involved with the majority of the failures occurring on the early Feb. surface hoar. In the central portion of the region a natural avalanche cycle to size 3.5 was observed on all aspects and elevations. At this point it's not surprising that the early Feb SH was to blame. As skies cleared Wednesdays, observers in the south of the region were able to get their eyes on a widespread avalanche cycle that occurred Monday & Tuesday producing avalanches to size 3. A party of skiers accidently triggered a size 2 avalanche in the Panorama backcountry. (Not within the resort boundaries) The avalanche was on a 35 degree slope, which is the average pitch of an intermediate/advanced run at a ski area, in other words, not very steep. The avalanche's crown measured 150 cm. This continues the trend from a very active natural avalanche cycle that reached it's height on Monday and is ongoing.From Monday/Tuesday, Size 3 avalanches were common, with some size 4. Timber fell. One remotely triggered avalanche triggered from 300m away caught my eye - it speaks to the propagation potential of the surface hoar now deeply buried. If this layer is triggered the avalanche will be big; this layer can be triggered from below so be mindful of overhead hazard. This layer will not go away in the next few days. Also, a sledder triggered a size 3 avalanche in the Quartz Creek area and while the machine is reportedly totaled, the rider is okay.There are two great observations from professionals working in the region recently. The first one can be found on the MCR, it talks about the widespread & sensitive nature of the SH in the Northern Purcells. You can start here and work your way into the March observations: https://www.acmg.ca/mcr/archives.asp The other is in the form of a youtube video which also deals with the surface hoar, highlighting the potential for remote triggering and large propagations when this layer fails. Check out the shooting cracks in the video. Another 50cm + of snow has fallen since this video was shot. https://www.youtube.com/watch?v=UmSJkS3SSbA&feature=youtu.be

Early this week, approximately 30 cm of storm snow fell across the region accompanied by winds out of the W/NW & W/SW at speeds capable of wind slab formation. Another 15cm arrived midweek. On Friday, before the arrival of the cold front, freezing levels topped out near 1800m & winds were strong out of the SW. A cohesive slab continues to settle over the mid-February surface hoar, which is now down 90 to 160 cm. Recent reports include whumpfing and cracking, and moderate but sudden compression test results. This persistent weakness is susceptible to remote triggering and has the ability to propagate in low angled terrain, and the overlying slab structure creates the potential for step-down avalanches. 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.