New snow will add to the size and reactivity of recently formed storm slabs. Very tricky conditions are expected on Saturday and conservative terrain selection is critical. In areas that get the most wind and new snow, the local hazard may be HIGH
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
The first in a series of storm systems will reach the region on Friday evening. 20-30cm of new snow is expected between Friday evening and Saturday evening. Freezing levels are expected to climb to around 1300m and winds are forecast to be moderate to strong from the southwest. The second storm system is expected to reach the region on Sunday and is forecast to bring another 20-30cm by Monday night. Freezing levels are expected to hover around 1500m and alpine winds should remain moderate to strong from the southwest. A bit of a break between storm systems is currently forecast for Monday with another storm pulse Monday night.
Avalanche Summary
On Thursday, natural avalanche activity up to size 2 was reported in the Pemberton area on north and east aspects. These were 30cm thick slabs releasing on a layer of surface hoar and facets. Explosives triggered a couple size 1.5 storm slabs in the Whistler area where the storm slab was only 10-20cm thick. Natural and human-triggered avalanches are expected to increase in size and reactivity as the storm progresses over the weekend.
Snowpack Summary
The new snowfall will add to the 20-40cm of storm snow from earlier in the week. This storm slab is sitting above a widespread layer of surface hoar, facets, and/or sun crust on steep south aspects. 10-20 cm below this is a second buried weak layer of surface hoar and/or a crust. The mid and lower snowpack is generally strong, with the exception of shallower snowpack areas that may be more faceted. At lower treeline elevations recent rains have saturated the upper snowpack. At higher elevations moderate southerly winds have recently loaded lee features at treeline and in the alpine.
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.