Wet, warm weather forecasted for Sunday means the potential for loose, wet avalanches in extreme terrain. Watch for pockets of storm slab in areas that receive snow instead of rain. Very strong winds are forecast Sunday morning at higher elevations.
Confidence
Low - Due to the number of field observations
Weather Forecast
Another warm and wet system will pummel the South Coast on Sunday before freezing levels drop with moderate snow accumulations into early next week.Sunday: Rain during the day (20-30 mm) before the freezing levels drop to 1000m (and possibly as low as 700m) in the evening with 10-15cm snow overnight. Strong to extreme south winds at ridgetop on Sunday morning. Monday: Flurries, accumulation 10-15 cm. Light to moderate southwest wind. Alpine temperature -1. Freezing level 1000 m.Tuesday: Snow, accumulation 20-30 cm. Moderate to strong south wind. Alpine temperature -1. Freezing level 1200m.
Avalanche Summary
No recent avalanches have been reported. However, the recent rain-on-snow event is suspected to have caused a natural, loose wet avalanche cycle. Although natural avalanche activity and human triggering potential has decreased with cooler temperatures, ongoing rain will maintain the potential for loose wet avalanches, particularly in steep, unsupported terrain. Storm slab development is also a concern at high alpine elevations where precipitation may fall as snow accompanied with strong winds.
Snowpack Summary
There is little information on snowpack structure at this time, except that recent heavy rainfall has saturated the upper snowpack at all elevations and washed away much of the snow at lower elevations. Travel below treeline is becoming more and more rugged, with many open creeks and early season hazards. Up to 30 cm of heavy wet snow may have fallen at the highest elevations (above 1400m) Friday into Saturday.Snow depth varies from 40 - 130 cm for elevations between 900 - 1200m across the region.
Problems
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.
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.