Purcells

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

The same weather pattern we've been in for the last few days persists for the foreseeable future as the Gulf of Alaska continues to steer a cool & unsettled airmass over the province. Saturday: Patchy skies in the morning before a relatively weak low pressure system slides across the region after lunch. Strong afternoon winds out of the SW at ridgetop, light winds treeline & below. Freezing level tops out at 1100m. 5 - 10 cm expected by Sunday morning. Sunday: Very light snowfall Sunday, skies clearing overnight. Freezing level near 1300m. Moderate ridgetop winds out of the west. Monday: Freezing level starts at the surface, climbing to near 1500m during the day. Winds at the high end of light at ridgetop out of the W, SW. Light winds at and below treeline. No significant precip forecasted.

Natural avalanches failing within the storm snow to size 2 on all aspects Friday. I've left some of the narrative in from last week as it offers a humbling look into the deep slab avalanche problem: On Friday, a very large avalanche was triggered by a cornice in Gorman Lake (Dogtooth Range). It was wide, deep and covered sled tracks. Photos here: https://bit.ly/GMOYCv . There were four other close calls in the Purcell Mountains last week, all involving very large slabs releasing either from a distance or with a light load. On Thursday, a snowmobiler remotely triggered a size 3.5 slab on an east aspect at 2400m at Oldman Creek, east of Quartz Creek (video here https://bit.ly/GLHIbg). It failed 1-2 m deep, was 200-300 m wide and ran full path, taking out mature timber. A second slope also failed, either remotely or sympathetically.

15 - 50 cm of snow has fallen in the last 48 hours, as of Friday afternoon. In wind exposed locations this new snow has been formed into wind slabs which could be up to a meter in depth in the north of the region. In the south these slabs are closer to 20 cm in depth. Below this lies a well settled snowpack. Spring the season has arrived, operators reported moist snow as high as 2500m on Wednesday. These warm temps have really helped to settle out the upper snowpack. Professionals throughout the region are reporting a very well settled & firm snowpack below the recent storm snow. The exception is slopes below 1000 meters, which have not refrozen for many days. These slopes received as much as 10mm of rain Wednesday night making them rain soaked and sloppy.The sun is forecast to make an appearance Saturday morning & Sunday afternoon. The spring sun is increasing in strength as each day grows by a few minutes. It takes very little time for S, SE & SW aspects to feel the heat of the sun now. W & E facing slopes are just starting to be affected by the sun as we head into the tail end of March. As soon as the sun comes out, watch for roller-balling & pin-wheeling to start surprisingly quickly. Wet point release avalanches won't be far behind on slopes receiving direct sun.There's a lot of strong snow between recreationists and the February surface hoar layers and there hasn't been a deep slab avalanche since Saturday March 24th. Deep slab avalanches till may be possible. I'm thinking of two different scenarios at the moment:1. The most likely scenario is a large cornice or icefall failure impacting the slope below and producing a very large avalanche. Managing this piece of the hazard puzzle is done by monitoring what's happening above you. Cornices or slopes receiving direct sun are suspect. If you feel like there's a question as to whether or not a piece of cornice is warming to its breaking point, then, there's no question, it's time to get off that slope. Pay special attention to this this phenomenon on Saturday.2. Last weekend an experienced party remote triggered a very large avalanche in Glacier Park near Mt. Tupper. At this point I think the probability of human triggering the deep slab is very low. I don't really want to be proved wrong though, as the result would be large and destructive avalanche 1.5 - 2 m in depth. The most likely location for this type of failure is where the snowpack goes from thick to thin. This is most likely near ridge crests, the edges of slopes and especially around rock outcroppings.