Regions
Banff Yoho Kootenay.
Excellent spring skiing continues with new snow in the forecast for Tuesday. Keep in mind that it is still possible to trigger the deep persistent facets in steep terrain, especially from thin areas or with large triggers such as cornices.
Weather Forecast
Unsettled spring weather could bring as much as 10-15cm of new snow on Tuesday with light SE winds and temperatures remaining cool. Freezing levels are forecast to stay below 1800m. A slight clearing trend and continued cool temperatures is forecast for Wednesday with a few more flurries.
Snowpack Summary
Another 10-15cm Sunday night brings the recent snowfall to between 20-40cm. This new snow is generally bonding well with some isolated pockets of wind slab in the alpine. Below tree line the surface snow is moist on solar aspects. At tree line and above a 120cm+ firm slab with few weaknesses overlies weaker basal facets in much of the region.
Avalanche Summary
A few loose moist avalanches up to size 1.5 were observed out of steep solar alpine terrain on Monday near Lake Louise. Explosive control produced a couple size 1.5-2 slab avalanches in the recent storm snow with minimal propagation. Ski areas reported being able to ski cut small wind slabs from the recent snow up to size 1 that were running far.
Confidence
Intensity of incoming weather systems is uncertain on Tuesday
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 Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.