With great powder comes great responsibility. Expect heavy sluffing with the new snow and recognize that danger has increased when you see signs of slab formation. This will happen more quickly at higher, wind-affected elevations.
Confidence
Moderate - Forecast snowfall amounts are uncertain
Weather Forecast
Tuesday night: Cloudy with continuing periods of snow bringing 10-15 cm of new snow. Light to moderate southwest winds.Wednesday: Decreasing cloud with easing flurries and a trace of new snow, with new snow totals around 40 cm. Light southwest or west winds. Alpine high temperatures around -10.Thursday: A mix of sun and cloud, with cloud increasing and flurries beginning in the evening. Light east winds. Alpine high temperatures around -7.Friday: Cloudy with continuing flurries and a trace to 5 cm of new snow, with new snow totals of around 10 cm. Light southwest winds. Alpine high temperatures around -6.
Avalanche Summary
Preliminary 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. Expect a continuation of this type of activity on Wednesday.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. This is the latest of several recent observations of persistent slab avalanches failing on the persistent weak layer that was buried in mid-January. The persistent weak layer producing these avalanches is described in the Snowpack Summary below.
Snowpack Summary
30-50 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 20-40 cm of snow from last weekend's storm 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 60 to 80 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.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.