These danger ratings are for the north of the region where triggering the buried persistent weak layer continues to be a concern. Danger may be lower in areas that do not have this problem.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Overcast with flurries, light southwest winds, and freezing levels down to 1000 metres overnight. Light snow with increasing southwest winds on Wednesday and daytime freezing levels up to 1600 metres. Light to moderate precipitation starting early Thursday with moderate to strong southwest winds and overnight freezing levels around 1300 metres. Freezing dropping back to valley bottoms by Friday morning. A weak ridge is expected to build on Friday, but we are un-certain regarding the amount of sunshine we will see.
Avalanche Summary
An early report on Monday of another skier remote triggered avalanche size 2.5 from 200 metres away on a southeast aspect at 2320 metres, believed to have released on the February 27th weak layer. A MIN report from Monday at Gorman lake in the Dogtooth range describes "a lot of cornice failures", as well as "many slides running full path." On Sunday, large cornice releases triggered persistent slabs on slopes below up to size 3.0 in the central part of the region, and a group of skiers remotely triggered a size 2.5 from 6 metres away on a southeast aspect at 2400 metres in the north of the region. On Saturday several natural and explosive initiated cornice failures to size 2.5 were reported. In the north of the region on friday control work produced several size 2 to 3 persistent slab avalanches on high elevation north through east facing features. These avalanches were failing on the mid and early February persistent weak layers.
Snowpack Summary
Recent moist surface snow has re-frozen into a crust at all elevations on solar aspects and up to at least 2000 metres on shaded aspects. Cornices continue to be described as large and fragile, and may fail with additional loading from forecast snow, or from high daytime temperatures. Some recent storm snow or wind slabs are likely to release as loose wet snow during periods of daytime warming. Buried persistent weak layers continue to be a concern for remote triggering in isolated areas where crusts are not strong enough to "bridge" the weakness. The late February surface hoar/crust weak layer is down 40-90 cm. This layer is still reactive to human triggers in some places while in other spots it's really tough to trigger, and there's not much of a reliable pattern telling us what exact aspects are most suspect. Deeper weak layers from mid-February and early January are now down 50-90cm and 70-120cm respectively. Triggering an avalanche on either of these layers has become unlikely but still has the potential to produce very large avalanches in isolated locations.
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.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.
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.