A big rise in freezing levels may mean that a deep persistent slab wakes up. A lot of uncertainty exists as to what this layer will do as temperatures climb. High levels of uncertainty are best managed by choosing conservative terrain.
Confidence
Moderate - Freezing levels are uncertain
Weather Forecast
Exact 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.FRIDAY NIGHT - Mainly cloudy / southwest winds, 10-20 km/h / alpine low temperature near -4 / alpine temperature inversionSATURDAY - Cloudy with sunny periods / southwest winds, 10-20 km/h / alpine high temperature near +3 / Freezing level 1500 m / strong alpine temperature inversion with above freezing temperatures possible to 3000 mSUNDAY - A mix of sun and cloud / southwest winds, 10-20 km/h / alpine high temperature near +5 / freezing level 3000 m / strong alpine temperature inversionMONDAY - Sunny with cloudy periods / southwest winds, 10-20 km/h / alpine high temperature near +5 / freezing level 3000 m / strong alpine temperature inversion
Avalanche Summary
Several explosives triggered avalanches to size 2.5 were reported in the region on Friday. Most of these were on northerly aspects in the alpine. One was on a southeast aspect at 2000 m.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 snow surface has likely frozen into a melt freeze crust below 1600 m, and a sun crust at upper elvations. 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.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.The deeper layers in the snowpack may become reactive this weekend with warm temperatures and sun impacting the snow.
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.
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.