Dangerous avalanche conditions are widespread. Thick storm slabs already blanket higher elevations, with lower elevations an increasing concern as new snow settles and forms slabs over weak layers at the old surface and deeper in the snowpack.
Weather Forecast
Wednesday night: Cloudy with clear periods. Light northwest winds.Thursday: Mainly sunny with cloud increasing and flurries beginning in the evening. Light southeast winds. Alpine high temperatures around -10.Friday: Cloudy with increasing flurries bringing about 10 cm of new snow by end of day, continuing overnight. Light southwest winds. Alpine high temperatures around -6.Saturday: Cloudy with continuing periods of snow bringing 10-15 cm of new snow by end of day, with new snow totals around 30 cm, flurries easing overnight. Light variable winds. Alpine high temperatures around -9.
Avalanche Summary
Improved visibility on Wednesday allowed for observations of numerous large (size 2-3) natural storm slabs on north to northeast-facing features in the Fernie area. Subsequent explosives control in the same area also yielded storm slabs up to size 2.5, mainly on northeast aspects. Ski cutting continued to produce storm slab and loose dry releases to size 1.5.Observations from Tuesday showed widespread loose dry and storm slab releases reaching size 1.5. These occurred naturally as well as with ski cutting and skier traffic. A report from the Flathead on Monday described continued observations of large whumpfs at 1700-1800 metres. This can be attributed to collapsing of the large, weak, January 17 layer of surface hoar. Collapses of this type on a sufficiently large and steep slopes can be expected to produce persistent slab releases.Another small (size 1) persistent slab was triggered by a skier in the western Flathead on Saturday. The slab was 40 cm deep and released from a northeast aspect at 1800 metres in an area that had not seen recent traffic. Several other small persistent slabs were triggered with ski cuts in the same area.
Snowpack Summary
30 to upwards of 50 cm of new snow has buried a variable surface of older wind-affected snow at wind-exposed treeline and alpine elevations, a new weak layer of feathery surface hoar in protected areas at lower elevations, and a thick melt-freeze crust below 1600 metres. Below the new snow, another 20-30 cm of older storm snow may sit on weak and feathery surface hoar crystals in shaded and sheltered areas.Above 1600 metres, the mid-January layer of surface hoar and/or crust is now buried around 70 to 90 cm deep. The surface hoar is found on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m. The melt-freeze crust is found on south aspects at all elevations. This layer was the subject of a recent Special Public Avalanche Warning and remains a serious concern as it adjusts to the load of new snow above it.The remainder of the snowpack is generally well-settled. Thin snowpack areas, such as in the east of the region, may hold weak and sugary faceted grains near the base of the snowpack.
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.
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
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.