Avalanche Forecast

Fair

Synopsis:  The region should see one last burst of precip as the moisture laden system moves off to the east Saturday night.  Sunday/Monday bring a drying trend that should persist through Monday evening. Saturday Night: 10/15 cm/mm snow/rain.  Freezing level around 1500 at Sunset, steadily lowering through the night. Moderate to Strong SW winds.Sunday:  Freezing level starts at 500m rising to 900m during the day.  No precipitation expected.  Cloudy skies.  Winds switch to the NE, light at treeline, strong at ridge top.  Monday: Freezing level at valley bottom.  No precip.  Clear skies.  Winds light and variable.Tuesday: Freezing level at valley bottom, rising to 1000m during the day.  Precip begins around lunch time as another deep upper low approaches the region.

A widespread natural avalanche cycle occurred on Friday with many reports of avalanches running up to size 4 on all aspects and elevations.  Remember that we define a size 4 as being large enough to destroy a railway car or semi truck.  The observations are humbling to say the least.

A heavy dump of moist new snow has added to recent storm totals (now 120-150 cm over a two-week period). The snow surface became wet as snow gradually turned to rain to approximately at 1900 m. I expect a crust to develop at lower elevations as temperatures drop Saturday night. Below the storm snow lies a highly reactive weak layer of surface hoar (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. 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 down 150 cm has been responsible for a couple of recent large, surprising avalanches. Immediately following the current storm, the presence of this deeper weak layer could further increase the potential size of avalanche events.