The storm may be over, but the mountains are currently primed for skier/sledder triggered avalanches.
Weather Forecast
Synopsis: The pineapple express will continue to deliver moisture laden air and significant precipitation through Saturday night before things begin to dry out on Sunday/MondaySaturday Night: 10/15 cm/mm snow/rain. Freezing level around 1400 at Sunset, steadily lowering through the night. Moderate to Strong SW winds.Sunday: Freezing level starts at 450m rising to 900m during the day. No precipitation expected. Cloudy skies. Winds switch to the NE, mod at treeline, strong at ridge top. Monday: Freezing level at valley bottom. No preicp. Clear skies. Winds light and variable.Tuesday: Freezing level at valley bottom, rising to 500m during the day. No significant precip. Cloudy skies. Winds become more organized out of the south as another deep upper low approaches the province.
Avalanche Summary
Visibility has been limited, as a result we don't have much in the way of avalanche observations from Friday. On Thursday, natural avalanches up to size 3.5 were observed on north and south aspects from 1500 m to 2200 m.
Snowpack Summary
This latest storm is really packing a punch, it's laid down around a meter of snow at this point, much of which is heavy and moist. The snow surface became wet as snow gradually turned to rain to approximately 1800 m in the south of the region and 1500 m in the north. I expect a crust to develop at lower elevations as temperatures drop Saturday night. Strong southwest winds have redistributed the new snow into deep wind slabs on exposed lee slopes and cross-loaded gully features. The February 12 persistent weak layer (crust, and/or surface hoar) is now down 60-100 cm. It is primed for triggering and has been reacting readily to both natural and human triggers on all aspects and a wide range of elevations. Deeper persistent weak layers from early February and late January continue to show planar failures when moderate to hard forces are applied in snow pack tests. These deeper layers have not been reactive to the weight of a rider, but they could potentially be triggered during or immediately after the present storm system, further increasing the potential size of avalanche events.
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.
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.