Snowfall amounts are highly uncertain for Saturday night. Pay close attention to how much snow falls in your riding area, and be prepared to back off to mellow terrain.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Saturday
Weather Forecast
Saturday night: 5-20cm of new snow / Variable winds / Alpine temperature of -13Sunday: Overcast skies with light flurries / Extreme northeast winds / Alpine temperatures of -20Monday: Mix of sun and cloud / Extreme northeast winds / Alpine temperatures of -22Tuesday: Mix of sun and cloud / Light north winds / Alpine temperatures of -20
Avalanche Summary
A few days ago, a large human-triggered avalanche was reported from Corbin (near Sparwood) on a wind affected slope in an area where weak facets were present. Evidence of a natural size 2.5 persistent slab avalanche was also noted on a treeline feature in the same drainage. While technically this area is in the Lizard/Flathead region, I feel as though it is indicative of conditions in the South Rockies. Where you get a combination of weak sugary snow lower in the snowpack and a supportive upper slab, conditions are ripe for avalanches to be human-triggered. When the wind picks up again on Sunday, new accumulations from Saturday night will get shifted into lee and cross-loaded features and we can expect an increase in wind slab avalanche activity
Snowpack Summary
Up to 20cm of new snow may fall on Saturday night. Extreme northeast wind are expected to redistribute these accumulations into wind slabs in exposed lee terrain. The new snow will overlie previously formed wind slabs which developed on Friday night and Saturday. In general, there is very little structure to the snowpack, with low-density snow sitting over soft sugary facets. Travel is very challenging as a result. A variable interface that formed during the cold snap in early December can be found buried 30-50 cm deep. This interface consists of weak faceted (sugary) snow and preserved surface hoar in sheltered areas. The interface is likely most reactive in wind-affected terrain where it is covered by hard wind slabs. The snowpack is a generally weak and faceted below this interface, including another weak layer with surface hoar or facets that was buried in early December. Hazards such as stumps, rocks, and open creeks are still a major concern.
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.