New snow and wind are creating deeper and increasingly destructive storm slabs ripe for human triggering. Sticking to simple terrain would be a great way to manage the elevated hazard on Thursday.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
WEDNESDAY NIGHT: 10-20cm of new snow / Moderate to strong southerly ridgetop winds / Freezing level around 500m.THURSDAY: 10-20cm of new snow / Moderate to strong southerly ridgetop winds / Freezing level dropping to 700m.FRIDAY: 5-10cm of new snow / Light to moderate southerly ridgetop winds / Freezing level around 500m.SATURDAY: 5-10 cm of new snow / Moderate southwesterly ridgetop winds / Freezing level around 500m.
Avalanche Summary
On Tuesday, a natural size 2.5 storm slab avalanche was reported near Whistler. It was reported as being about a day old and no further information was reported.Looking forward, forecast snow and wind will promote ongoing surface storm slab avalanche activity, while surprisingly deep releases within (or at the base of all of the recent storm) snow may be possible in isolated terrain.
Snowpack Summary
The region has been pummeled by heavy snowfall and extreme southerly winds. 20 cm of new snow on Wednesday morning continues to be redistributed by strong southeasterly winds. Last weekend's storm likely created dense storm slabs lurking in lee and cross-loaded features. Impressive cornice growth is also expected to have occurred.About 180cm below the surface you'll find a crust that was buried mid-January and is present at all elevations. This crust is thin on northerly aspects and up to 3 cm thick on solar aspects. Most reports suggest an improving bond at this interface, but the load of the new snow may tip the balance and reactivate this layer in isolated terrain. Below this, the snowpack is generally strong and well-settled.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.