Kootenay Boundary

Fair - Timing or intensity of solar radiation is uncertain on Sunday

Warm temperatures, sunny skies and light winds are expected to continue for the forecast period. The inversion is expected to weaken and narrow by Sunday. The Columbia Valley and other areas near large bodies of open water may continue to experience valley cloud. Some areas may continue to experience above freezing temperatures in the alpine overnight. All areas are expected to experience strong solar radiation and daytime warming.

There were some large deep avalanche releases on Friday. Most of the large avalanches were on solar aspects, as a result of warm overnight temperatures combined with daytime heating. There were also a couple of large avalanches that released on northerly aspects that were caused by cornice falls releasing slabs that stepped down to the ground. Also, there were a couple of large avalanches in the southern interior that released naturally or with light triggers on northerly aspects that released down to the ground or glacial ice. I decided to leave the information from the previous bulletin, as I think it shows the trend of larger avalanches. Explosive control in the Kaslo to New Denver highway corridor on Thursday produced several size 2.5 moist releases that pushed storm snow to the middle of the runout of 2 km long paths. These slides started between 2000 and 2300 metres on S-SW aspects. A larger explosive controlled avalanche occurred at Bear Lake from a SE aspect in the alpine. The avalanche was size 3.5 dry slab with an average crown of 160 cm and ran full path, 1100 vertical metres for 2.5 km. Reports of loose dry sloughing in steep terrain from several operators in the area up to size 1.5. Explosive control at Kootenay Pass produced several avalanches size 2.5-3.0 on cross loaded slopes with crowns between 50-100 cm.

Temperatures dropped below freezing at higher elevations on Friday night. New sun crusts are developing on steep solar aspects. Warm air trapped in the alpine caused temperatures to remain above freezing on Thursday night above about 2100 metres. Pin-wheeling and other signs of moist snow have been observed on solar aspects at and above treeline. Continued warm temperatures in the alpine may trigger buried weak layers on solar aspects. Steep planar slopes with shallow snowpacks are the most suspect. The recent storm snow layer is about 30-50 cm thick and is quite variable across the region. There are a couple of thin crusts buried below the storm snow that have been producing moderate to hard shears in tests. Some areas are still getting sudden planar shears on the mid-december surface hoar layer.