Storm snow from the past few days has formed slabs at treeline and in the alpine. These may become more reactive to human triggering as temperatures rise, especially if the sun comes out.
Confidence
Moderate - Freezing levels are uncertain
Weather Forecast
Freezing levels and alpine temperatures are difficult to forecast in the coming days with mild temperatures and temperature inversions dominating the weather pattern this weekend.THURSDAY NIGHT - Mainly cloudy with isolated flurries / southwest winds, 10-25 km/h / alpine low temperature near -4 / freezing level 1100 m / alpine temperature inversionFRIDAY - Mainly cloudy with isolated flurries / southwest winds, 10-30 km/h / alpine high temperature near 0 / Freezing level 1500 m / alpine temperature inversionSATURDAY - A mix of sun and cloud / southwest winds, 20 km/h / alpine high temperature near +2 / freezing level 3000 m / alpine temperature inversionSUNDAY - Sunny with cloudy periods / southwest winds, 20-30 km/h / alpine high temperature near +3 / freezing level 3000 m / alpine temperature inversion
Avalanche Summary
Several explosives triggered avalanches to size 2 were reported on southeast and northeast aspects between 1850 m and 2100 m on Thursday.A size 1.5 natural storm slab avalanche was reported on Wednesday.
Snowpack Summary
15-30 cm of recent new snow combined with mild temperatures and strong winds has formed storm slabs at alpine and treeline elevations. The new snow sits on previous storm snow and wind slabs above 1500 m, and a melt freeze crust below 1500 m.In sheltered areas around treeline, 70-120cm of recent snow may sit on a weak layer of surface hoar (feathery crystals). In the east of the region near Corbin, a persistent weak layer that formed in early December may still be found 90 to 150 cm deep. This layer mostly consists of faceted (sugary) snow with some isolated areas also containing surface hoar. While professionals are still tracking this layer, it has not been reactive for some time now. However, the warming event that is forecast in the coming days may wake this layer up.There is a mix of crusts and facets that formed in late October/early November near the bottom of the snowpack. This layer may only be an issue on steep slopes where the snowpack is shallow.
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.