Stormy weather is forecast for the next few days. Expect new storm slabs to develop and watch for reverse loading if the wind is out of the East.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Thursday
Weather Forecast
Overnight: 5-10 cm of new snow with moderate southeast winds and freezing down to 1000 metres. Thursday: 3-5 cm of new snow with winds becoming moderate southwest. Daytime freezing up to 1800 metres. Friday: Another 3-5 cm of new snow with moderate westerly winds and daytime freezing up to 1400 metres. Saturday: A few more cm of new snow with moderate southwest winds and a chance of sunny breaks in the afternoon. Daytime freezing up to 1400 metres.
Avalanche Summary
Natural cornice falls to size 2.0 and explosives control to size 3.0 were reported from the central part of the region on Tuesday. Explosive control and natural triggers released cornices up to size 3.0 in the central part of the region on Monday. One cornice failed during explosives control when the shot was dropped onto the cornice structure resulting in a size 2.0 that did not release a slab on the slope below.
Snowpack Summary
Recent moderate to strong winds have redistributed new snow into wind slabs on a range of aspects at higher elevations. Fragile new cornice growth also occurred along ridgelines over the course of the week. The new snow has buried melt-freeze crusts on all aspects below about 2200 metres and in the high alpine on solar aspects. Isolated surface hoar may be found below the new snow on shaded aspects at high elevations. Below the new snow interface, a number of storm snow and crust layers that formed over mid to late March appear to be well bonded. At higher elevations, the February crust/facet layer is now down around 130-150 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These layers were active during a storm in mid-March and produced some very large avalanches. Occasional deep releases were also reported in late March and early April, keeping these layers an ongoing concern.
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.
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.