Tuesday's danger ratings are based on about 15cm of new snow. If new snowfall amounts are greater than 20cm in your riding area, the avalanche danger may be High.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Tuesday
Weather Forecast
Tuesday: 15-30cm of new snow / Strong westerly winds / Freezing level at valley bottomWednesday: Overcast skies and light flurries / Moderate westerly winds / Freezing level at valley bottomThursday: 5-10cm of new snow / Moderate westerly winds / Freezing level at valley bottom
Avalanche Summary
There were reports of a few very soft slabs failing over steep rolls on Sunday. These avalanches occurred in response to locally moderate amounts of new snowfall on Saturday. Of note, there was a a size 2 persistent slab avalanche triggered on an east facing alpine feature on the north side of the highway in Roger's Pass. The avalanche, which was reported to have failed on the mid-December weak layer, was remotely triggered from a distance of 30 metres. Although this seemingly isolated avalanche occurred in a different forecast region, this event may point to a pattern of increased activity on the mid-December layer which may also extend into the South Columbia region. With new snow and strong winds forecast for Monday night and Tuesday, I'd also expect new wind slab activity in higher elevation terrain on Tuesday.
Snowpack Summary
On Tuesday, new snow and wind are forecast to form fresh wind slabs in exposed higher elevation terrain. 40-70 cm of snow now overlies the mid-December interface which consists of a variety of old snow surfaces including wind affected snow, faceted (sugary) crystals, and/or surface hoar crystals. Recent tests suggest the the new snow is well bonded to the interface in most areas. However, this layer is still reactive in some snowpack tests and should be investigated before pushing into steeper terrain. Limited observations from the North Columbia region suggest this layer may be especially touchy on the eastern side of the Selkirks. The thick mid-November crust layer typically sits 1-2 m down in the snowpack. Recent test results on this layer suggest it is generally well bonded to the adjacent snow with the possible exception of shallow snowpack areas. This layer is considered dormant at this time but remains an isolated concern that we will likely be tracking through much of the season.
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.