A buried persistent weak layer may roar back to life over the next few days as the freezing level rises and the sun comes out. South facing slopes are especially suspect and are best avoided at this time.
Summary
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Monday
Weather Forecast
Monday, most of BC will receive partly cloudy conditions with a few lingering flurries in the Columbia mountains. A warm system makes landfall Tuesday morning, which should open the door to rain and wet snow into the alpine on Tuesday and Wednesday.MONDAY: Broken cloud cover, freezing level beginning around 1300 m rising to about 1800 m, light west/southwest wind, trace of precipitation possible. TUESDAY: Scattered cloud cover, freezing level beginning around 1800 m rising to about 2500 m, light to moderate south/southwest wind, trace of precipitation possible.WEDNESDAY: Scattered cloud cover, freezing level beginning around 1500 m rising to about 1700 m, light southwest wind, trace of precipitation possible.
Avalanche Summary
Avalanche activity on Saturday was limited to small storm slabs and sluffing in steep terrain.Warming temperatures on Friday initiated loose wet avalanche activity to size 1.5 on a variety of aspects. Small storm and wind slabs were sensitive to skier triggering on steep unsupported features at upper elevations too. On Thursday warming temperatures initiated large loose wet avalanches to size 3 on south facing aspects between 2100 and 2700 m in the neighboring Glacier National Park. A natural size 2.5 wet slab was observed on a southeast facing feature at 2200 m as well.
Snowpack Summary
5 to 15 cm of new snow fell Saturday with moderate southerly wind. This snow rests on a crust that is present on all aspects below 2000 m, and extends up to about 2500 m on south facing aspects. The storm snow be be sitting on surface hoar on polar aspects (north and east) at upper elevations. The main concern is the mid-March Persistent Weak Layer (PWL) which is now 60 to 110 cm below the surface. This layer is composed of a crust on all aspects at low elevations. At upper elevations the layer presents as a crust on solar aspects (those that face south and west) and buried surface hoar on polar aspects. The reactivity of this interface has been steadily decreasing and while the likelihood of triggering a deeper persistent slab avalanche is lowering, the consequence of doing so remains high. Solar aspects are expected to be the most suspect as the freezing level begins to rise over the next few days.Deeper persistent weak layers from January and December are still being reported by professional observers, but are generally considered dormant.
ghelgeson,
Avalanche Canada
