Avalanche Forecast

Fair - Due to variable weather conditions

5 - 10 cm are expected Wednesday evening before a fast moving convective storm impacts the region Thursday bringing 10 -15 cm by Friday morning, with the southern portion of the region receiving slightly more. Winds Thursday will be out of the W starting the day near 30 km/h, increasing to 40 gusting 70 in the afternoon. Freezing level stays around 1600m. Friday: The system exits the region but not before leaving 5 - 10 cm of snow with continued strong winds. There may be afternoon sunny periods with the freezing level remaining near 1500m. Saturday: The ridge intensifies resulting in high intensity solar input for the region with just light winds at upper elevations. The freezing level starts the day around 500m, climbing to 1500m in the afternoon.

On Tuesday operators in the south of the region reported thin windslabs 10 - 20 in depth that were failing naturally at all elevations. Very little activity was reported from the north of the region. 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: http://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 http://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.

5 - 15 cm of new snow fell Monday evening, which has been formed into soft wind slabs10 - 20 cm in depth. This snow rests on a variety of old surfaces. Before the new snow, professional operators in the Purcells were reporting moist snow below 2000 m and wet snow below 1900m. The old snow surface, now down 10 - 20 cm consists of a suncrust to ridgetop on S, SW & SE facing slopes & a melt freeze crust to 2000 m on all other aspects. The recent warm temps have really helped to settle out the upper snowpack. Professionals throughout the region are reporting a very well settled & firm upper snowpack below the recent storm snow. The exception are slopes below 1000 meters, which did not refreeze Tuesday evening. These slopes are likely rain soaked at this point too, making for a sloppy wet snowpack at lower elevations. 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.The effect of the sun becomes very important at this time of the year. We're expecting a few cm's of snow everyday through Friday. 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 it's been a few days since there was a large deep avalanche in the region. That being said, it could still be triggered. I'm thinking of three 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.2. There was an outbreak of large human triggered avalanches last week, see the avalanche observations for the details of these incidents. This makes me think that it may still be possible for skiers or sledders to trigger very large avalanches failing 1.5 - 2m 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.3. While I don't foresee it occurring in the next few days, a slope that does not experience an overnight refreeze is suspect for producing large avalanches. This is something to think about as we flip our calendars to the April page.