Warm temperatures and sunny skies forecast for the next few days will have a significant weakening effect on the snowpack. If solar radiation is particularly strong the avalanche danger could rise to HIGH.
Confidence
Fair - Timing or intensity of solar radiation is uncertain on Saturday
Weather Forecast
A ridge of high pressure will continue to dominate the region bringing dry conditions and mainly clear skies for the foreseeable future. Winds should be light to moderate from the west on Saturday, becoming light and northwesterly on Sunday and Monday. An inversion is expected for Saturday bringing valley cloud and alpine temperatures reaching +5.0. More seasonal temperatures are expected for Sunday and Monday.
Avalanche Summary
Steep solar aspects saw numerous loose wet and slab avalanches on Thursday with some occurrences to size 3. On the same day in the south of the region, a snow cat was working on ridge and remotely triggered a size 3 deep slab avalanche from 30m away. The avalanche, which failed on basal facets, occurred on a southeast facing slope at 2160m.I would expect more loose wet activity and cornice fall with real potential for deep slab activity with continued warming.
Snowpack Summary
Parts of the forecast area have received up to 90cm of storm snow which has been blown into dense windslabs in exposed areas. The new snow overlies a variety of old surfaces, the most reactive of which appears to be the Jan 8th surface hoar. There are reports of "sudden" test results on this layer, now buried anywhere from 55cm to 90cm below the surface. There are 2 other layers of note which professionals are keeping a close eye on: The late-November persistent weak layer consists of a sun crust on steep south facing slopes and surface hoar in sheltered areas and may sit well over 200cm below the surface. At the base of the snowpack you may also find the October persistent weak layer which consists of facets sitting on a crust. This layer is predominantly found on northerly aspects at tree line and in the alpine. The depth of both these layers makes skier triggering unlikely (maybe a heavy load on a thin spot in steep terrain, a cornice fall or rapid warming). The consequences of triggering any of these weaknesses would be severe..
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.
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.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.