Regions
Banff Yoho Kootenay.
Increased solar input and a weak freeze will likely cause an increase in natural activity. Watch locally for heating, and minimize overhead hazard. SH
Weather Forecast
Freezing levels to 2000m and valley highs in the East over 10C with a decent amount of solar input. No new snow and light to moderate W winds. A slight temperature inversion with increasing winds will develop Saturday. 3000m temperatures will rise to just below freezing. A cooling trend will set in on Sunday.
Snowpack Summary
15-25 cm of recent storm snow sits over a well settled100cm+ slab which sits precariously over weak basal facets at treeline and above. Tests show easy to moderate sudden collapse results in the facets. The surface snow is of a mix of soft snow in the shade, melt-freeze snow below treeline, and sun crust on sun exposed slopes.
Avalanche Summary
No new avalanches reported today, except for lots of smaller loose, wet slides at treeline and below on solar aspects in steep terrain as the day warmed up .
Confidence
Timing or intensity of solar radiation is uncertain on Friday
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.