Forecast sun and warm daytime temperatures are a concern for rapidly changing the cold winter snowpack. Choose conservative terrain without overhead hazards.
Summary
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
A ridge of high pressure is building over the province. Clear overnight with freezing down to valley bottoms and moderate northwest winds. Clear with strong solar radiation on Thursday with daytime freezing levels climbing up to 1500 metres. Another good freeze expected for Friday morning under clear skies. Daytime freezing levels rising up to 1700 metres with strong solar and light winds. Variable freezing level on Saturday morning, somewhere between valley bottoms and 1000 metres (valley dependant). Uncertain about sun or cloud on Saturday, weather models are not in agreement; the models do agree that the freezing level will rise up to at least 2200 metres.
Avalanche Summary
No new slab avalanches reported, some loose dry sluffing continues to be reported from steep shaded aspects. On Monday there was a sled triggered avalanche in the Mt Mackie area southwest of Castlegar that resulted in a fatality. The slab avalanche was size 2.0 at 1900 metres on a northerly aspect, the crown was approximately 100 cm deep and appeared to fail on the February 27th buried surface hoar. There was also a skier accidental size 2.5 that started as a cornice failure and propagated down to one of the buried crusts; this was near Red Mtn in the Rossland range. There were also a couple of natural avalanches and a skier accidental avalanche size 2.0 in the eastern part of the region near Nelson. The storm snow continues to be a concern for human triggering, and avalanches that start in the storm snow may "step-down" to deeper buried weak layers. Cornices are also a concern for natural avalanches and human triggering.
Snowpack Summary
The recent storm snow is 40-60 cm deep and continues to settle above a mix of crusts at treeline and below. In some drainages these storm slabs may be sitting on a thin crust that was initially buried on March 11th. A second curst, (the early March melt/freeze crust) can be found down 50 to 80 cm. The late February (Feb 27th) persistent weak layer of buried surface hoar down 70-120 cm continues to result in large avalanches. I suspect that this weak layer is more prominent on northerly (shaded) aspects at 1700 metres and above. This surface hoar layer may be associated with a crust on solar aspects. With forecast sun and strong solar radiation, triggering this deep weak layer may be more likely. Watch for moist or wet surface snow as a sign that solar radiation is strong and deep weak layers may become reactive.
triley,
Avalanche Canada
