Thursday's storm came in with moderate southerly winds that likely formed wind slabs up high which may rest on surface hoar, facets and/or crust. It may be calendar spring, but it's winter in the mountains, be very cautious in wind affected terrain.
Confidence
Moderate - Due to the number of field observations
Weather Forecast
A cold and unstable pool of air is allowing for cooler than normal temperatures and also driving convective precipitation that should continue through Friday night. A bit of clearing is in store for Saturday before cloud builds back into the region Sunday. FRIDAY NIGHT: Freezing level at 600 m, moderate southwest wind, 5 to 10 cm of snow.SATURDAY: A few clouds, freezing level beginning at 500 m rising to 1000 m, light variable wind, no significant precipitation expected. SUNDAY: A few clouds in the morning building to broken cloud cover in the afternoon, freezing level holding at about 600 m, light west/southwest wind, no significant precipitation expected.MONDAY: Overcast, freezing level beginning around 600 m rising to about 1000 m, light southwest wind at 2000 m, moderate to strong west/northwest wind at ridge top, 2 to 4 mm of precipitation possible.
Avalanche Summary
Very little avalanche activity has been reported form the North Shore mountains where the storm began as rain and then transitioned to snow. In the alpine, new snow and wind Wednesday night into Thursday likely initiated natural storm slab avalanche activity.
Snowpack Summary
Around 45 mm of precipitation fell Thursday into early Friday morning. Rain transitioned to snow above 1000 m Thursday morning which produced about 25 cm of snow with light to moderate east/southeast wind. The warm to cold nature of the storm has allowed the new snow to bond well to the old surface up to treeline, but little is currently known about the alpine. The alpine likely saw very little if any rain and more snow/wind. Up high the new snow is thought to be sitting on a mixture of weak grains including a crust on solar aspects and potentially facets/surface hoar on polar aspects. Below any recent snow accumulations, the overall snowpack is well settled and strong.
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.