New snow and wind beginning late Saturday afternoon will increase avalanche hazard. If however, the storm arrives earlier than forecasted, hazard ratings will also increase sooner.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
TONIGHT: Mostly clear. Ridge wind light to moderate, west. Alpine temperature near -5. Freezing level valley bottom.SATURDAY: Increasing cloud, snow beginning in the afternoon. Accumulation 5-15 cm. Ridge wind moderate to strong, south. Alpine temperature near -3. Freezing level 1000 m.SUNDAY: Cloudy, flurries. Accumulation 5-10 cm by Sunday morning. Ridge wind moderate to strong, west. Temperature near 0. Freezing level 1800 m.MONDAY: Mix of sun and cloud. Ridge wind moderate, west. Alpine temperature near 0. Freezing level 1800 m.
Avalanche Summary
Numerous small slab avalanches have been reported in the top 10-25 cm of snow all through this week. It appears as though moderate amounts of new snow with just the right amount of wind have continuously set up thin, but touchy wind slabs in a variety of places. While these have been mostly small (size 1), a size 2 wind slab avalanche was reported near Fernie on Wednesday morning on a northeast aspect at approximately 2000 m.Explosive control work on Friday produced wind slab and cornice releases up to size 2 in alpine terrain.Thursday in the Elkford area, recent small (size 1) loose/dry avalanches were reported on northerly aspects while loose/wet were observed on solar aspects.Also, cornices are large along ridgetops and were actively failing last week.
Snowpack Summary
20-30 cm storm snow sits above a variety of crusts on all but high north aspects. Wind has formed isolated slabs in lee features, and in some cases snow may be poorly bonded to the crusts.There are some reports of a surface hoar layer roughly 80 cm deep on north aspects at treeline, but no recent avalanche activity on this layer. A layer of sugary facets around a crust exists near the bottom of the snowpack, but this layer has been inactive for some time.
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.
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.