Regions
Kootenay Boundary.
Wednesday is a day of transition. The snowpack will see a final test of warm air and light rain before cooling temperatures have a stabilizing effect.
Weather Forecast
Wednesday: Cloudy with scattered wet flurries bringing 5-10 cm of new snow. Moderate to strong south winds. Freezing level dropping from about 2500 to 1500 metres over the day. Alpine high temperatures around 0.Thursday: Mainly cloudy. Light northwest winds. Freezing level to 1600 metres with alpine high temperatures around -2.Friday: Cloudy with flurries beginning in the evening. Light northeast winds. Freezing level to 1600 metres with alpine high temperatures of -3.
Avalanche Summary
Avalanche activity through the end of the weekend into Monday focused on a natural solar induced loose wet avalanche cycle on south and west aspects in the alpine an treeline to size 2. On Friday reports indicate numerous size 2-2.5 natural and explosive controlled storm snow avalanches running on all aspects in the alpine and at tree line. There were also several skier triggered storm slab avalanche size 1.5-2 both Friday and Saturday on north aspects in the alpine and tree line.
Snowpack Summary
Light rain transitioning to wet flurries should bring 5-10 cm of new snow by Wednesday afternoon. This new snow will accumulate on a variable surface of crust and moist snow.Last week's snow has settled and been redistributed by predominantly west and southwest wind on upper shady aspects or has become moist or wet and/or refrozen (depending on the time of day) on slopes facing the sun. On sheltered northerly aspects it may be sitting on a layer of surface hoar.A mix of weak layers exist 50-100 cm below the surface, including small surface hoar on shady aspects and a crust on solar aspects. These layers have consistently been reactive in snowpack tests, suggesting they could potentially remain reactive to human triggers as well. Deeper weak layers that formed in January and December have gained strength and gone dormant at this time. They include several surface hoar and facet layers 1 to 2 m below the surface and a crust/ facet interface near the base of the snowpack.
Problems
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.