Regions
South Coast Inland.
Fresh snow will be touchy in wind affected terrain on Friday, while another wet storm is lined up to elevate the danger this weekend.
Confidence
Moderate - Track of incoming weather systems is uncertain on Saturday
Weather Forecast
FRIDAY: Isolated flurries before the next storm arrives Friday evening, strong southwest winds, alpine temperatures around -7 C.SATURDAY: Storm starts Friday night and delivers 15-25 cm, strong southwest winds, freezing level up to 1500 m with alpine temperatures around -4 C.SUNDAY: Clearing skies following the storm as alpine temperatures drop to around -10 C, moderate west winds.
Avalanche Summary
On Wednesday, evidence of a recent widespread natural avalanche cycle was reported in the northern part of the region. The avalanches included several size 2-3 storm slabs, a number of which stepped down to weak layers over a metre deep. Large cornice failures were also reported. One small skier triggered avalanche was reported on a north-facing wind loaded feature at 1950 m. There are no recent reports from the southern part of the region.On Friday, the most recent snow is expected to form new wind slabs in exposed terrain that may bond poorly to a buried rain crust. It has become difficult to trigger the February weak layers but there is still a chance that a smaller wind slab avalanche or a cornice fall could still step down and release a persistent slab avalanche.
Snowpack Summary
By Friday morning expect 10-20 cm of recent snow sitting above a widespread layer of wet snow up to about 2100 m. The wet snow layer is likely turning into a crust and may become a weak layer as storm snow accumulates. Strong south winds are likely forming wind slabs in the lee of exposed terrain, which may bond poorly to the crust. In the north of the region, the February weak layers are now down 80-120 cm. The layer of buried surface hoar has recently produced a few persistent slab avalanches. The crust/facet layer appears to be gaining strength but may also still be reactive in isolated areas. In the Coquihalla area, the crust/facet layer is down well over 1 m and appears to have gone dormant.
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.