Warm temps, strong to extreme SW winds and an additional 20cm of new snow overnight is producing widespread storm slabs in open terrain. Conservative terrain choices are a must at this time. A avalanche cycle is ongoing at this time.
Confidence
Fair - Due to limited field observations on Wednesday
Weather Forecast
Snowfall amounts, winds and temperatures are all expected to fall as a high pressure system begins to push into the region bringing with it cooler air. Expect temperatures to begin to fall overnight and into the day on Thursday. Daytime highs on Thursday are expected to be in the -15C range with light winds out of the north.
Avalanche Summary
No new observations on Wednesday but conditions were obscured for most of the day.
Snowpack Summary
An additional 20cm of new snow over the past 24hrs with strong SW winds. Widespread storm slab development in Alpine terrain and in all open areas at treeline. 35-40cm of recent storm snow can now be expected throughout the forecast region. The 0106 Surface hoar/facet interface is down 40-50cm and extensive cracking was being observed on this layer on Tuesday. The 1106 rain crust at the base of the snowpack should be in skiers minds as there is a potential for avalanches to step down to this interface. Cornices were growing quickly on Wednesday with the warm temps, new snow and strong winds.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
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.