Precipitation and high freezing levels will be driving the avalanche danger on Thursday. Surprisingly large avalanches are possible especially if the region receives significant rainfall.
Confidence
Moderate - Freezing levels are uncertain on Thursday
Weather Forecast
WEDNESDAY NIGHT: Up to 5mm of precipitation / strong southwest winds / freezing level at about 2000m THURSDAY: 5-10mm of precipitation / strong southwest winds / freezing level falling from 2000m to about 1500m FRIDAY: light flurries / moderate southwest winds / freezing level at 1500m SATURDAY: mix of sun and cloud / light to moderate northwest winds / freezing level at 1000m
Avalanche Summary
Small loose dry and loose wet sluffs were observed in the Crowsnest Pass area on Tuesday. In addition to a small wind slab avalanche in a lee alpine feature, there was also evidence of recent natural cornice failures. Looking forward, new snow and wind on Thursday is expected to spark a round of wind slab activity at higher elevations. At elevations where precipitation falls as rain, loose wet avalanches may be likely.
Snowpack Summary
Up to 30 cm of recent storm snow sits on a melt-freeze crust on southerly aspects and lower elevation terrain, surface hoar on sheltered slopes, and older wind affected surfaces in exposed terrain. Widespread wind effect is evident in the alpine with fresh wind slabs forming in exposed lee terrain. Warming has Cornices have grown significantly recently. A layer of buried surface hoar can be found between 50 and 70cm down and remains a concern, primarily west of the Continental Divide. Below 1500-1600 m the snowpack is essentially isothermal and very spring-like. The snowpack rests on a weak crust/facet layer from early December.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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 Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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.