Recent storm snow and strong winds have built reactive slab avalanches. Conservative route selection is crucial.
Confidence
Moderate - Wind speed and direction is uncertain on Wednesday
Weather Forecast
A surface ridge sets up on Wednesday over the Interior mountains bringing mostly cloudy and dry conditions. Ridgetop winds will blow strong and steady through Wednesday then start to back off Thursday night through the weekend. Wednesday: Mostly cloudy with alpine temperatures -6 and southwest winds 30-50 km/h.Thursday: Cloudy with snow amounts 5-15 cm. Alpine temperatures -6 and ridgetop winds southwest gusting to 55 km/hr.Friday: Isolated flurries with alpine temperatures -7 and ridgetop winds light from the southeast.
Avalanche Summary
On Monday, numerous natural slab avalanches were reported up to size 2.5 from a variety of aspects and elevations. Natural avalanche activity may taper Wednesday, however; skier triggered avalanches are likely.
Snowpack Summary
Up to 50 cm of storm snow sits above a plethora of old snow surfaces including wind affected snow, faceted (sugary) crystals, surface hoar crystals and a thin sun crust on steep solar aspects. The new snow will likely have a poor bond to these old surfaces. Deeper in the snowpack exist two potentially weak layers that may become reactive under the new load from the recent storm snow. The first being a spotty surface hoar layer down 40-80 cm and the mid-November crust that sits 100-200 cm down. Recent test results on these layers have varied from moderate and sudden to hard and resistant, and in some cases no result. In shallower snowpack areas faceting is happening below and above the crust. Tracking and monitoring this potentially weak interface is crucial as it adjust to the new load of snow above it.
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.
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.