Continued heavy snowfall is expected to create widespread reactive storm slabs. Very conservative terrain selection is critical and travel in avalanche terrain is not recommended.
Confidence
Moderate - Due to the number of field observations on Saturday
Weather Forecast
Snowfall is expected to continue Saturday overnight and into Sunday. Weather models are currently showing the potential for another 30-50cm of snowfall by the end of the storm. On Sunday, freezing levels are expected to be at around 500-700m and alpine winds are forecast to be moderate from the southwest. On Monday, dry conditions are expected with a mix of sun and cloud. Freezing levels are forecast to fall back down to around sea level and alpine winds should be light from the northwest. Sunny, dry, and cold conditions are currently expected for Tuesday.
Avalanche Summary
On Friday, a size 1.5 skier triggered avalanche was reported on the MIN. The slab was 20-30cm thick and the avalanche was 30-40m wide. By the end of the storm on Sunday, parts of the region could see storm slabs 60-80cm thick. These slabs are expected to be reactive to human triggering, especially in wind loaded terrain. Natural avalanches are expected during periods of heavy snowfall.
Snowpack Summary
As of Saturday afternoon parts of the region have seen 40-60cm of new snowfall, with a lot more expected by Sunday afternoon. The new snow is falling on a variable surface that includes settled snow on southerly aspects, loose snow on shaded aspects, isolated pockets of surface hoar, and sun crusts on steep solar aspects. Overall the incoming snow will likely bond poorly to this interface. The thickest and most touchy storm slabs can be expected on north-facing wind-loaded features. An old rain crust was down 30-50 cm prior to the storm, and reports had suggested that the snow above it was poorly bonded to the crust on some shady north aspects. Below the crust, the snowpack is 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.