We're in a period of uncertainty as cooling temperatures gradually stabilize the snowpack. Continue avoiding large avalanche paths and overhead hazards.
Weather Forecast
Monday: Cloudy with sunny periods early in the day. Light east winds. Freezing level to 1500 metres with alpine temperatures around -6. Tuesday: Cloudy with scattered flurries bringing approximately 5 cm of new snow, mainly in the evening. Light southeast winds. Freezing level to 2000 metres with alpine temperatures around 0. Wednesday: Mainly cloudy with scattered flurries and a trace to 5 cm of new snow. Strong southwest winds. Freezing level to 2000 metres with alpine temperatures around 0.
Avalanche Summary
Reports from Saturday included observations of one naturally triggered Size 3 deep persistent slab as well as numerous natural storm slab releases occurring on northeast to northwest aspects just west of Fernie. Reports from Friday showed explosives triggered persistent slabs (and one storm slab) running from Size 2.5-3. Crown fractures generally ranged from 100-200 cm. On Thursday, storm slabs were observed releasing naturally to Size 2, with explosives control yielding deep persistent slabs to Size 3. Most crown fractures measured about one metre but one impressive storm slab featured a three metre fracture depth. North to northeast aspects were the main performers over both days.Looking forward, recently formed storm slabs and cornices in the high alpine will likely remain reactive to natural and human triggering on Monday, especially while the sun is out. The heightened avalanche activity shown by the above reports is expected to gradually decrease, but the scale and extent of this activity demands that backcountry users take caution with that assumption.
Snowpack Summary
Stormy weather on Saturday formed fresh storm slabs at high alpine elevations while rain once again saturated the snowpack at lower alpine elevations and below. Lower temperatures have since formed a roughly 10 cm thick crust at the rain soaked surface, which will tend to break down with daytime warming at lower elevations and on solar aspects. Isolated basal facets still exist in shallow snowpack areas and still carry the potential to produce destructive full-depth avalanches. Possible triggers for these deeper weak layers include cornice falls and storm slab avalanches, which may trigger naturally with daytime warming.
Problems
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.