South Rockies

A sudden change in weather can have surprising effects on the snowpack. Conservative terrain use is key.

Moderate - Freezing levels are uncertain on Tuesday

TUESDAY: Scattered flurries with up to 5 cm of new snow, extreme southwest winds, freezing levels rising to 1500 m and likely higher on the eastern slopes.WEDNESDAY: Scattered flurries with up to 5 cm of new snow, strong southwest winds, freezing levels rising to 1700 m and likely higher on the eastern slopes.THURSDAY: Clearing with isolated flurries, strong southwest winds, freezing level around 1500 m.

On Sunday, a natural size 1.5 wind slab was reported on a northeast aspect. An MIN report from Waterton Park on Friday shows a large size 3 deep persistent slab avalanche triggered by a smaller wind slab on a feature with highly variable snow depths. Although an isolated event, this avalanche highlights the possible consequence of our tricky persistent slab problem, especially with the incoming change of weather.

Increasing winds are causing widespread wind affect in exposed alpine and treeline terrain and forming reactive wind slabs on lee features. The mid pack is quite variable throughout the region and the structure depends on snow depth. In deeper snowpack areas, the snowpack appears to be well settled and right side up with isolated concerns for the mid-December facet layer found 50 to 80 cm deep. In shallow snowpack areas and lower elevations, the snowpack is heavily faceted and there are concerns for the mid-December weak facet layer as well as weak basal facets. If a persistent slab is triggered from thinner snowpack areas it may release on the basal facets resulting in a full depth avalanche. Triggering these deeper weak layers will become more likely this week as warm temperatures soften the overlying slab.