Wind stiffened storm slabs are expected to form Friday night into Saturday at upper elevations. These slabs may be resting on a slight crust which could make them that much more sensitive to human triggering.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Saturday
Weather Forecast
Rain is expected to turn to snow Friday night as the freezing level lowers and a couple of weak residual lows bring patchy light precipitation to the coast through the weekend.FRIDAY NIGHT: Freezing level beginning around 1800 m, lowering to 1500 m by dawn, moderate southwest/west wind, 5 to 15 cm of snow expected at upper elevations.SATURDAY: Overcast, freezing level around 1400 m, light to moderate south/southeast wind, 1 to 5 mm of precipitation expected.SUNDAY: High cloud, freezing level around 800 m, light south wind, 1 to 3 mm of precipitation expected.MONDAY: High cloud, freezing level around 900 m, light south wind, 3 to 6 mm of precipitation expected.
Avalanche Summary
On Friday several loose wet avalanches released naturally below 2000 m in elevation. Professionals conducting control work were able to ski cut avalanches to size 1.5 in the alpine. Snowballing and pinwheeling from steep rocky terrain was also observed.
Snowpack Summary
Rain Friday reportedly soaked the upper 15 to 20 cm of the snowpack and left all aspects with moist snow on the surface from valley bottom to at least 2000 m, maybe even ridgetop. As temperatures begin to cool Friday night we can expect a thin melt freeze crust to form on the surface. New snow and wind Friday night into Saturday will likely allow for the formation of fresh storm slabs on this crust at upper elevations.Up to 100 cm below the surface there is a widespread melt-freeze crust that was buried on December 15th. This layer has not produced much in the way of avalanche activity and is likely trending towards dormancy. Beneath the mid-December crust, the lower snowpack is generally strong and well settled.
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.