Sun and warm temperatures are expected to increase the avalanche danger.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
Some cloud overnight with a chance of convective flurries, and freezing levels dropping to valley bottoms. Mix of sun and cloud on Thursday with moderate northeast winds and 2-3 cm of new snow. Clear on Friday with strong solar radiation, light winds and daytime freezing levels up to 1700 metres. Clear on Saturday with moderate southwest winds and freezing levels rising up to at least 2200 metres.
Avalanche Summary
In the Crowsnest north area, previous natural cornice falls had not released any slab avalanches on the slopes below. Cornices were reported to be smaller in the Smith basin area. On Monday our field team in the Crown Mtn area observed a natural cornice fall size 2.0 that did not release a slab on the steep slope below. The field team also observed the debris from a previous cornice fall that probably released over the weekend. On Saturday a few natural cornice failures to size 2 were observed in extreme terrain. On Friday a few different very large avalanches (to size 3.5) were observed that failed naturally on southerly facing alpine features. These avalanches were likely triggered by falling chunks of cornice impacting thin snowpack areas in the far north of the region. Debris ran down the track well into the below treeline vegetation band.
Snowpack Summary
On Wednesday the field team was in the Crowsnest north area around Window Mtn, where they found 155 cm of snow on the ground at 2250 metres on a north aspect. The foot penetration was 35 cm, but the light winds were not transporting this available snow today. Ski penetration was about 15cm. In Smith Basin on Tuesday, our field team found a thinner snowpack with only 140-200 cm on the ground. They found about 10 cm of recent storm snow above a 2 cm breakable crust that was not supportive. The March 7th crust in Smith basin was down about 20 cm, with decomposing snow below that becoming facetted weak crystals deeper in the shallow weak snowpack. There were no notable test results, and evidence of aggressive slope testing on east-south-west aspects that did not trigger any releases. On Monday at 1920 metres in the Crown Mtn area there was 17 cm of new snow above a breakable 2 cm crust. Below the crust there was dry snow at this elevation. We estimate the crust extends up to about 2000 metres. Strong southwest winds have created widespread wind slabs at treeline and above.
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.
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 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.