Continued unsettled weather is expected to keep avalanche danger elevated, especially at higher elevations in wind exposed terrain.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain on Sunday
Weather Forecast
A cool unstable airmass moves into the region Saturday evening, which should deliver 1 to 8 cm of snow by daybreak Sunday. Sunday offers a brief break in the action before a second pulse arrives Sunday night. SUNDAY: Freezing Level starting around valley bottom, rising to 1500 m, 0 to 2 cm of snow during the day, moderate southwest winds. SUNDAY NIGHT: Freezing level holding at 1500 m, 2 to 15 cm of snow, moderate to strong southwest winds. MONDAY: Freezing level around 1500 m, trace of snow, moderate to strong southwest winds. TUESDAY: Freezing level starting around valley bottom, rising to 1500 m, no significant snow accumulations expected, light west / northwest winds.
Avalanche Summary
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. Natural cornice failures were also reported Friday to size 1.5. Reports from Thursday are limited but include skier-controlled size 1 wind slab avalanches. Natural wind and storm slab avalanche activity was expected on Thursday in response to heavy loading from snow, wind and rain.
Snowpack Summary
Approximately 25 cm of fresh snow is bonding poorly to a widespread supportive crust, with the most recent snow-line reaching 1800m in the Elk Valley. In exposed terrain, widespread very touchy wind slabs lurk below ridge-crests, behind terrain breaks and in chutes. Deeper in the snowpack, recent tests gave very easy sudden collapse results down 80cm on a southeast aspect at 1850m 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
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.