A variable dose of new snow has resupplied avalanche problems in much of the region. Be mindful of avalanche danger increasing in sync with daytime warming.
Weather Forecast
Wednesday night: Mainly cloudy. Light to moderate southeast winds.Thursday: A mix of sun and cloud. Light variable winds. Alpine high temperatures around -2 with freezing levels to 1900 metres.Friday: Mainly sunny. Light northeast winds shifting northwest. Alpine high temperatures around 0 with freezing levels to 2100 metres.Saturday: Mainly sunny with cloud increasing over the day. Light southwest winds. Alpine high temperatures around 0 with freezing levels to 2100 metres.Overnight freezing levels will increase steadily during this period, dropping briefly each night to between 1000 to 1500 metres.
Avalanche Summary
No new avalanches were reported in the Purcells on Tuesday, but reports from neighbouring regions showed new snow from Tuesday's storm reacting to skier traffic, ski cutting, and explosives control with 10-25 cm-deep slabs propagating easily and widely over previous surface crusts. All aspects were represented in reports, with a focus on north to northeast aspects as a result of loading by southwest winds. Similar conditions are likely to exist in areas of the Purcells that received more than a skiff of new snow from Tuesday's storm. Looking forward, lingering wind slabs (in areas with new snow) may still react to skier triggering and may also become touchier with warming. In some areas an ample supply of new snow is in place to reinvigorate loose wet avalanche problems as sunshine and warming take hold each day. Where less new snow exists, loose wet activity may be slightly more subdued.
Snowpack Summary
Variable new snow amounts of a trace to 25 cm have accumulated above a surface of melt-freeze crust in most areas above 1500 metres. Below this elevation it buried variably moist or crusty surfaces. Precipitation as rain has continued to saturate the snowpack that is increasingly isothermal (slushy and cohesionless) and disappearing rapidly below about 1100 metres.The mid snowpack is generally consolidated and strong, but exceptions may exist on north aspects above 2000 m, where a gradually strengthening layer of faceted grains buried 40 to 60 cm deep may still be preserved below an overlying slab of old and hard wind-affected snow.The base of the snowpack is composed of weak faceted snow which may coexist with a melt-freeze crust. Only one very large persistent slab was reported to have failed at this layer during last week's warming event.
Problems
Loose Wet
Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.