Watch for new wind slab development on Saturday. Forecast snowfall amounts are uncertain, so pay close attention to how much snow falls in your area, and choose terrain accordingly.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
Up to 12cm of new snow is forecast to fall on Saturday with another 5cm possible in the overnight period. Generally light accumulations (~5cm) are forecast for Sunday and Monday. Ridgetop winds should be moderate from the south on Saturday, becoming light on Sunday and Monday. Freezing levels should sit at about 1800m on Saturday, and then drop closer to 1500m for the rest of the forecast period.
Avalanche Summary
On Thursday numerous naturally triggered wind slabs (mostly in the size 2 range) were observed at treeline and in the alpine. They occurred in response to new snow and wind. On Friday explosives control continued to produce storm slabs to size 2.5 on a variety of aspects throughout the region. Of note, a size 2.5 persistent slab avalanche was triggered with explosives in the Dogtooth Range. The mid-February layer was the likely culprit in the avalanche.
Snowpack Summary
Snowfall accumulations on Thursday were in the 10-20cm range. Strong southerly winds redistributed these accumulations into touchy wind slabs at treeline and in the alpine. 30-70 cm recent storm snow overlies a prominent weak layer buried on or around Feb-27. The deepest snow amounts appear to be in the west central area near Kootenay Lake. The Feb-27 weak layer comprises surface hoar and a crust. It has been widely reported but recent snowpack test results are mixed, with some tests indicating this layer is gaining strength, while others indicating it can still fail with sudden "pop" results. A deeper weak layer from mid-February is now down 50-80cm. The early January surface hoar/facet layer is typically down 70-120cm. Triggering an avalanche on either of these layers has become unlikely but either still has the isolated potential to produce very large avalanches with a heavy trigger.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.