Regions
Northwest Coastal.
Tricky winter conditions exist at higher elevations. Localized solar radiation, snow and winds will destabilize 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
The next pacific front hits the North and Central coast Thursday evening bringing anywhere from 5-15 mm. Lingering cloud, periods of sunshine and convective snowfall may occur on Friday. Ridgetop winds will be light from the West and freezing levels near 1100 m. Saturday and Sunday will be mostly cloudy with light precipitation. Ridgetop winds will be light from SW and freezing levels rising to 1300 m Saturday. Warm moist air will reach the North on Sunday and freezing levels will rise to 2300 m.
Avalanche Summary
On Wednesday, numerous size 1.5 slab avalanches were reported. They failed on NW-N aspects above 1400 m. On Tuesday, the region saw a natural cycle up to size 3 was from steep alpine and treeline terrain. Suspect some of these naturals are stepping down to the old interfaces buried April 9 th and mid- March. With continued snow, rain, and strong winds natural avalanches and human triggered avalanches will likely continue. Lower elevations have become rain soaked and natural loose wet avalanches from steeper terrain features are expected.
Snowpack Summary
At upper elevations 35- 80 cm of settling storm snow has blanketed the region. The new snow has been redistributed by strong south-west winds into wind slabs on leeward slopes and terrain features. 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 is reportedly unreactive, however; with the new load of wind and snow this should remain on your radar as 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.