Expect new wind slabs to develop with forecast winds and new snow available for transport. Minimise exposure to cornices at this time.
Confidence
Moderate - Wind speed and direction is uncertain on Tuesday
Weather Forecast
Moderate to strong westerly winds overnight with 2-3 cm of new snow and freezing levels down to valley bottoms. Some convective flurries expected during the day Tuesday with moderate westerly winds and freezing levels rising up to 1500 metres. A good freeze is expected on Wednesday morning before freezing levels climb up to 1500 metres during the day under mostly clear skies and light winds. Clouding over Wednesday night with 5-8 cm expected by Thursday morning with moderate northeast winds. A mix of sun and cloud on Thursday with light winds.
Avalanche Summary
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
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 moist snow at this elevation. We estimate the the crust extends up to about 2000 metres. Strong southwest winds have created widespread wind slabs at treeline and above. Deeper in the snowpack, recent tests gave very easy sudden collapse results down 80 cm on a southeast aspect at 1850 m on the deep persistent facet/crust weakness that was buried early December. Watch this weakness with extreme warming from sun-exposure, or warming/loading from rain. Cornices are also reported to be huge and weak. Check out the latest SoRo field team video on Instagram: @avcansouthrockies
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.