South Columbia

Very dangerous avalanche conditions exist in the backcountry. Avoid all avalanche terrain!

Fair - Timing, track, or intensity of incoming weather is uncertain

Synopsis: Starting Thursday night, a Pineapple Express will bring moisture to this region through the forecast period. Due to the narrow moisture stream, some areas may see more or less than the stated amounts below.Thursday night. 10-15 cm new snow, with the possibility of local enhancement. Very strong SW winds.Friday: Heavy snow/rain, with up to 30 cm/mm in the north of the region and more like 10-20 cm in the south. Freezing level around 1700 m. Southwesterly ridgetop winds to 70 km/hSaturday: Generally light snow/rain (around 5 cm/mm), higher amounts possible. Also the possibility of a brief period of clear weather. Freezing level around 1600 m. Southerly winds around 30 km/h. Sunday: Moderate to heavy snow (15-20 cm). Freezing level around 1400 m. Light winds.

On Wednesday, a size 2.5 avalanche was triggered by a group of skiers in the Monashees in open treeline glades at 1800 m on a south aspect. The bed surface was the Feb 12th surface hoar/crust layer. Also on Wednesday, two large avalanches (size 2 or 3) were remotely triggered from a flat ridge in the Monashees, one on Wednesday and one on Tuesday, both with a fracture depth of 130 cm. In both cases, there was steep north facing terrain directly below the ridge and the weak layer was found to be the Jan 26th surface hoar/crust weak layer. Additional natural and human triggered activity was noted in both the Monashees and Selkirks to size 3. On Tuesday, there were a good number of natural and human-triggered avalanches on all aspects reported up to size 3, mostly running on the February 12th surface hoar. Natural activity appeared to be triggered either by wind activity (mostly north and east aspects) or during periods of solar activity (southern aspects). Human triggered avalanches were easy and in some cases, surprising.The number, size, and destructive potential of recent avalanche events speak loudly to the touchy nature of the avalanche problem at this time.

Around a metre of storm snow now sits on a highly reactive weak layer of surface hoar layer (and/or a crust) which was buried on February 12th. Strong southwest winds have redistributed the new snow into deep wind slabs on exposed lee slopes and cross-loaded gully features. The February 12 layer is primed for triggering and has been reacting readily to both natural and human triggers on all aspects and a wide range of elevations. The effect of a large storm on the snowpack, particularly one accompanied by warm temperatures, wind and possibly rain, will be dramatic. Deeper persistent weak layers from early February and late January continue to show planar failures when moderate to hard forces are applied in snow pack tests. In particular, in the Monashees, a rain crust buried at the end of January approximately 130 cm has been responsible for a couple of recent large, surprising avalanches. During the upcoming storm, the presence of deeper weak layer could further increase the potential size of avalanche events.