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 Thursday
Weather Forecast
Generally clear skies are expected for the forecast period as a ridge of high pressure becomes established over much of the province. Winds are forecast to be light to moderate from the northwest becoming southwesterly on Saturday. Daytime alpine temperatures are expected to hover between 0.0 and +5.0.
Avalanche Summary
Several natural storm slab avalanches to size 3 were reported in the region on Tuesday, most occurring in alpine terrain on various aspects. I would expect avalanche occurrences to include loose wet activity with the potential for deeper slab activity with forecast warming on Thursday
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 directly triggering an avalanche on them unlikely (maybe a heavy load on a thin spot in steep terrain), but the consequences would be large and destructive.
Problems
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
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.
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.