The storm is moving across the interior regions tonight resulting in HIGH avalanche danger by morning. Heavy snowfall and strong winds are expected to develop new storm slabs.
Confidence
Fair - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A moist Pacific storm is moving into the region from the Southwest on Sunday. Expect strong Southwest winds overnight and 10-20 cm of new snow by Monday morning. Winds should become moderate Northwest during the day Monday with periods of flurries or light snow. Winds becoming moderate Westerly Monday evening as the next pulse of moisture moves into the region bringing 10-20 cm by Tuesday morning and another 10-15 cm during the day. Warm air and strong Southwest winds are expected on Wednesday at the end of the storm. Freezing levels should be at valley bottoms until Wednesday afternoon when they are expected to rise to about 1300 metres.
Avalanche Summary
No new avalanches reported. Forecast new snow and wind is expected to develop a reactive new storm slab.
Snowpack Summary
Forecast new snow and wind is expected to develop a new storm slab. There is about 30-50 cm of recent storm snow combined with variable winds that have produced windslabs on all aspects in the alpine and at treeline. Pockets of warm air in the north have likely made the snow dense in some places, while predominately westerly winds have set up fresh wind slabs in exposed lee areas. The persistent mid-December crust/surface hoar layer appears prominent in the south of the region and is still reported to fail easily during snowpack tests. It is most prominent at within a few hundred metres of treeline elevation. On average it can be found around 60 cm below the surface, although it has variably been reported anywhere from 30-90 cm below the surface. In the north of the region, this layer is present, although reported to be harder to trigger. Further down, a hard rain crust with facets from early November is buried more than a metre down and is currently unreactive. However, triggering from shallow rocky and unsupported terrain remains a concern.
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.
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.