Regions
Northwest Coastal.
Weak buried layers of surface hoar in the top 100 cm of the snowpack continue to be a concern for triggering slab avalanches.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
No precipitation forecast until at least Monday night. Clear skies with warm air above about 1100 metres on Saturday and Sunday. Moderate to strong southerly upper winds over the weekend, unsure if this wind will be low enough to affect local terrain and transport loose snow. Monday starting off clear with cloud and southeast wind building during the day. Temperatures around -10 in the valleys of the south and closer to -20 in the north of the region.
Avalanche Summary
No new avalanches reported. Commercial operations cautioning new wind slabs at ridge lines developing with outflow winds.
Snowpack Summary
Solar radiation has started to affect the surface snow on southerly aspects, resulting in loose moist or wet releases and the beginnings of melt-freeze crusts overnight. The recent 25-40cm of storm snow continues to facet due to the cold temperatures, and new surface hoar has been reported on all aspects and at all elevations. The forecast temperature inversion looks like it will be strongest on Friday, and our uncertainty revolves around how much warmth upper elevations will receive. It is also unclear how storm slabs, especially those sitting on buried surface hoar layers (in the top 100 cm) will react to the warming. I suspect that outflow winds are transporting unconsolidated snow, and areas that are having or have received wind may continue to have wind slab problems. The winds have been variable across the region; Shames has reported very little wind and slightly west of there the wind effect has been widespread. The north of the region has been cold with temperatures around -20 in the valleys and alpine temperatures around -8 at 2000 metres. Watch for weak basal facets in colder and shallower snowpack areas.
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.