The new snow and strong wind is expected to form new wind slabs that will bury the rain crust. If more than around 30 cm of snow accumulates in your riding area, a more widespread storm slab problem may develop and local hazard could be High.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Thursday
Weather Forecast
Light to moderate snowfall is expected Wednesday overnight and for most of the day on Thursday. 20-30 cm is expected during this period. Freezing levels are expected to be around 600 m early Thursday morning and reach around 1000 m in the afternoon. Alpine wind is forecast to be moderate to strong from the southwest for most of the day. Snowfall is forecast to continue Thursday overnight and during the day on Friday with the current forecast for another 10-20 cm. Freezing levels are forecast to remain below 1200 m during this period and alpine wind should remain moderate to strong from the south and southwest. The last significant storm pulse is currently forecast for Saturday with 20-40 cm currently forecast during the day.
Avalanche Summary
On Tuesday, two natural size 1.5 wet slabs were observed on a north aspect at 1150 m in the Whistler area. Natural and skier triggered loose wet avalanches were also reported. On Monday, natural storm slab avalanches up to size 1.5 were observed west of Bralone. In the Whistler area, explosives were triggering storm slabs up to size 2 and a skier triggered a size 1.5 storm slab on a north aspect at 2100 m elevation. Most of this storm slab activity had slab thickness of 20-30 cm but one was 80 cm thick in a wind loaded pocket. A natural cornice release was also reported on a northeast aspect at 2300 m. On Thursday, the new snow will bury the widespread surface crust and is expected to form new wind slabs in exposed terrain. It has become difficult to trigger the mid-February crust/facet layer but there is still a chance that smaller wind slab avalanches or cornices could still step down and release a persistent slab avalanche. At lower elevation, rain may result in wet sluffing from steep terrain features.
Snowpack Summary
On Tuesday, freezing levels reached at least 2200 m and rain was reported to at least 2000 m. As temperatures dropped on Wednesday, a new surface crust has formed at higher elevations. The new snowfall on Thursday will bury this crust layer and strong winds are expected for form new wind slabs.The mid-February crust/facet layer is now typically down 80-120 cm and in wind loaded terrain, it may as deep as 200 cm. With a thick layer of weak faceted snow above it, this crust layer was producing easy, sudden results in snowpack tests prior to the warming event. The layer is expected to gain strength with the cooler temperatures but there is a lot of uncertainty as to how long this layer will remain reactive. Below the crust layer, the mid and lower snowpack are well settled and strong.
Problems
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.
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.