The danger ratings don't tell the whole story. Uncertainty regarding the Deep Persistent Slab problem would have me avoiding any large or committing features.
Last week's storm snow has been redistributed by variable winds into wind slabs. They could have a poor bond to the crusty snow surfaces below.
Be cautious at ridge crests, on convex rolls, and in cross-loaded features.
Wind slab avalanches could step down and trigger the deeper persistent slab.
Natural cornice fall is possible with solar radiation. As natural avalanches taper off, cornices could still be sensitive to a human trigger.
Cornice fall could be a hazard on its own and it could trigger a deeper slab avalanche from the slope below.
The early December crust can be found 100-270 cm deep.
This deep persistent slab problem has been less active over the weekend, but we have been reminded multiple times in the last month that this layer could remain a concern all winter.
Thin rocky start zones are the most likely place to trigger this layer. Also, daytime warming, solar radiation, cornice fall, and step-downs from smaller avalanches could increase the chance of an avalanche on this layer.
Sunday Night: Mostly cloudy. Possible trace of snow expected. Light southwest wind trending to moderate northwest at higher elevations. Freezing level dropping to near valley bottom.
Monday: Mostly cloudy, possible clearing in the afternoon. ~3 cm of snow expected. Light northeast wind with periods of strong at higher elevations. Freezing levels rise to 1000 m, alpine low around -6 C.
Tuesday: A mix of sun and cloud. No new snow expected. Moderate southwest wind trending to strong northwest at higher elevations. Freezing levels drop to valley bottom overnight, rise back to 1000 m by the afternoon.
Wednesday: Partly cloudy. Possible trace of snow expected. Moderate southwest wind, trending to extreme northwest at higher elevations. Freezing levels drop to valley bottom overnight, rise back to 1000 m by the afternoon.
On Saturday, avalanche control with explosives produced a couple of small windslab avalanches around treeline. Also, neighbouring Waterton National Park reported a few natural windslab avalanches to size 2 on solar aspects in the alpine.
On Friday, several wind slabs and storm slabs up to size 2 were reported. A natural cornice fall also occurred pulling a size 1.5-2 storm slab in the fans on the slope.
Surface hoar up to 10 mm has been reported around Fernie. At this time it is unknown if this surface hoar growth is more widespread. Expect to find patchy sun crust on steep, solar aspects below treeline. The previously forecasted above freezing layer seemed to be less prominent and at a higher elevation than originally expected, but this sun crust could also exist in the high alpine.
Up to 15 cm of new storm snow fell Thursday with fairly light winds. Moderate to strong winds from the southwest on Friday stripped some windward slopes, and formed variable wind slabs. These slabs are up to 60 cm thick in lee features.
Around 2200 m and below, these windslabs overlie a crust buried on January 18th, which caps a dense 15 to 30 cm of settled snow. The crust varies with aspect and elevation from thin (2 cm thick) in the alpine to (4 cm) thick below treeline. Below this, the midpack is well consolidated above the early December crust/ facet interface.
The most notable layer of concern in the snowpack is a widespread crust that was formed in early December and is now down 100-270 cm. With warming last week this deep persistent slab problem woke up and produced several very large avalanches. Daytime warming, solar radiation, smaller avalanches, and cornice fall could continue to play a role in triggering deep persistent slabs.
