Regions
Northwest Coastal.
Cloud cover, warm alpine temperatures, localized solar radiation, and rain will deteriorate the snowpack. Use a conservative approach to terrain and watch for signs of instabilities.
Confidence
Fair - Due to the number of field observations
Weather Forecast
Most of the North Coast regions will see unsettled conditions through the weekend. A dominating ridge of high pressure over southern BC will push North by late Sunday keeping a well-organized storm offshore. Saturday will see mostly cloudy skies and ridgetop winds light from the SW. Alpine temperatures will rise to 3 degrees and freezing levels will be near 1300 m. On Sunday, light precipitation and moderate SW winds is expected. Influence from the upper level ridge will see freezing levels rise to 2400 m through Monday and rain up to 10 mm. By late Monday, the ridge starts to break down allowing a more seasonally westerly flow.
Avalanche Summary
On Thursday, numerous natural slab avalanches up to size 2 were reported and a widespread loose wet avalanche cycle occurred when the sun poked out in some areas. A larger size 3 slab was seen from across the valley at Shames, maybe a day old or so by now. On Tuesday, the region saw a natural cycle up to size 3 was from steep alpine and treeline terrain. Reports suspect that some of these naturals are stepping down to the old interfaces buried April 9 th and mid- March. With temperatures rising into the alpine, cloudy skies and light rain forecast, the snowpack will deteriorate and natural avalanche activity will continue. Lower elevations which have become rain soaked and natural loose wet avalanches from steeper terrain features are expected.
Snowpack Summary
At upper elevations 35- 80 cm of recent storm snow has blanketed the region. The new snow has been redistributed by strong south-west winds into wind slabs on leeward slopes and solar aspects may have a new sun crust. The lack of bond between the new wind slabs and storm slabs over the older snow surfaces buried on April 9 th (surface hoar, crusts and facets) is the primary concern. The March 25th persistent surface hoar / crust layer reportedly became reactive with the recent storm, however; observations are very limited and it may have just been in a localized area. With forecast warming well above mountain peaks this pwl should remain on your radar, it may re-awaken, initiating very-large and destructive avalanches. Moist- rain soaked snow exists at lower elevations.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.