Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Regions
Banff Yoho Kootenay.
The first major avalanche cycle of the season starts on Wed and peaks on Thurs. Avoid all avalanche terrain. There is a significant weak layer deep in the snowpack that is active and we expect widespread avalanche activity over the next two days.
Weather Forecast
A strong westerly flow dominates the region with the Pineapple Express bringing a big warm up and rain for Wed and Thurs. Expect 20cm of fresh snow by Wed afternoon and warming through the day - by Wed night freezing levels will reach 2600m and Thurs will be a heavy storm day with rain, snow, warmth and strong winds. Cooling beings late Thurs.
Snowpack Summary
The Little Yoho valley has a 100cm snowpack at 1750m. The top 60cm is dry, settled storm snow overlying facets on the Halloween crust - this is the layer to watch. Snowpack tests indicate sudden collapse failures on this layer and propagation can be expected. Strong winds with this next storm will create windslabs in exposed areas at TL and above.
Avalanche Summary
No new avalanche activity observed or reported Tues in the Little Yoho valley, Lake Louise resort or Sunshine Village area. Mon saw significant avalanche activity with Lake Louise ski resort reporting 32 avalanches releasing from 38 target areas controlled; several large avalanches up to size 2.5 - this shows the potential of the Halloween crust.
Confidence
Problems
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.
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.
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.