Wednesday's danger ratings are based on overcast skies. If the sun makes an appearance, consider the avalanche danger to be higher than posted.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain on Wednesday
Weather Forecast
Wednesday: Clear skies in the morning with increased cloud throughout the day / Strong southwest winds / Freezing level at 2500mThursday: 5-10cm of new snow / Strong southwest winds / Freezing level at 2100mFriday: Clearing skies / Light southwest winds / Freezing level at about 1800m
Avalanche Summary
Recent observations have been limited; however, a size 2 solar-triggered slab avalanche was observed at 2000m in the Elkford area on Tuesday. It was thought to be about a day old. For Wednesday, warm temperatures can be expected to promote instability within the snowpack. As the warm temperatures persist, and especially if we don't experience refreezing overnight, the potential for deep persistent slab releases will rise steadily each day. Any avalanches releasing on a basal weakness will likely be large and very destructive.
Snowpack Summary
Roughly 10 cm of new snow received late last week has been redistributed into wind slabs by strong southerly winds at upper elevations. Where it hasn't blown away, this new snow now lies above the 15-30 cm of dense snow that fell over the region on Thursday, which was mixed with periods of rain at lower elevations. Together, these more recent accumulations overlie the 90cm of low density storm snow that we received last weekend. Strong shifting winds redistributed this previous storm snow in exposed terrain, forming wind slabs over a variable old surface which includes wind affected surfaces, facets, and/or a rain crust below around 1500 m. The bond at the interface between this older storm snow and the previous surface is suspected to be improving slowly.In deeper areas, the snowpack appears to be well settled with only isolated concerns about the mid-December facet layer which was buried 50-100 cm deep prior to the weekend storm. In shallow snowpack areas and at lower elevations, the mid to lower snowpack is weak, faceted, and has no structure. In these areas the snowpack's weakness may reach a tipping point as warm temperatures persist over the coming days.
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.
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.
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.