Watch the temperature and solar warming this weekend, heat and/or direct sun could quickly initiate cornice fall and natural slab avalanche activity.
Weather Forecast
Synopsis: A ridge builds into the interior this weekend making for a fairly unexciting weather weekend. Look for high cloud, moderate freezing levels and no significant precipitation.Saturday: Freezing Level: 500m - 900m; Precipitation: Nil; Treeline Wind: Light, S | Ridgetop Wind: Moderate, WSunday: Freezing Level: 900m - 1400m; Precipitation: Trace; Treeline Wind: Light, NW | Ridgetop Wind: Moderate, NWMonday: Freezing Level: 1500m; Precipitation: Nil; Treeline Wind: Calm | Ridgetop Wind: Light, W
Avalanche Summary
On Thursday explosive control work in the region produced avalanches to size 2. A very soft slab was reportedly very sensitive to human triggering on steeper south aspects below 1800m, running on the March 19 crust.On Wednesday a size 2 wind slab was accidentally triggered by a skier in the southeast corner of the region. The avalanche occurred on a northeast aspect at about 2600m.
Snowpack Summary
15 - 50 cm of new snow has fallen in the last 48 hours accompanied by strong southwest winds which has created fresh windslabs in lee terrain. Below the new snow is a well settled storm slab which overlies a hard rain crusts. This crust exists on all aspects below 2000m and on solar aspects in the high alpine. North of Sparwood and in the Crow's Nest Pass area the buried crust seems more specific to previously sun-exposed slopes. The deep facet/crust persistent weakness buried at the beginning of February (now down up to 150cm) seems unlikely to trigger in areas where the hard, supportive near-surface crust exists. No matter where you are in the region, this weakness should stay on your radar as any activity at this interface would be large and destructive. Possible triggers include a large cornice fall, a large input in a thin snowpack area or solar warming.Cornices have also become large and unstable.
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.
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.