A complex set of avalanche problems is affecting the region. Old and new wind slabs on a variety of aspects as well as persistent slabs all demand your careful evaluation.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Tuesday
Weather Forecast
Sunday night: Flurries delivering 10 cm of new snow with light to moderate southwest winds.Monday: Flurries bringing another 5-10 cm of new snow. Winds moderate to strong from the southwest. Freezing level to 1000 metres with alpine temperatures around -6Tuesday: Cloudy with sunny periods and isolated flurries bringing another 5-10cm of new snow. Winds light gusting to strong from the northwest. Freezing level back to valley bottom with alpine temperatures of -11.Wednesday: A mix of sun and cloud with isolated flurries and a trace of new snow. Winds light from the west. Alpine temperatures to -17.
Avalanche Summary
No new avalanches were reported on Saturday, but new snow over Sunday and Monday is expected to form touchy slabs in the lee of exposed terrain features. Recent reports include a spooky size 3 natural avalanche spotted in the Liverwurst bowl on a north aspect at 1800m on Friday. See the MIN report for details and an image that will help to keep deep persistent weaknesses on your mind. The crown is approximately 150cms high and the failure may have been on basal facets, which are large, sugary, and weak.
Snowpack Summary
After light snowfall over the last couple of days, significant new snow over Sunday and Monday will continue to bury a variable snow surface that includes wind slabs as well as sastrugi and hard slabs. Surface hoar up to 20mm was reported to be growing on the surface in some areas before Thursday's light snowfall. The previously mentioned wind slabs formed after recent arctic outbreak winds scoured snow from a wide range of aspects, creating deposits on the lee side of exposed features. These wind slabs sit on a variety of older wind-affected surfaces at treeline and in the alpine and recent snowpack tests of wind slab layers have yielded increasingly resistant results. Cold temperatures may have a role to play in this, as they have promoted faceting in the upper snowpack with the effect of breaking down the cohesion of wind slabs. Deeper in the snowpack, the mid-December persistent layer (facet interface) has been more prominent and reactive in the Corbin zone than closer to Fernie. Take extra caution in thinner snowpack areas and areas of crossloaded snow where a smaller wind slab avalanche could step down to trigger this layer.
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.