Temperatures are expected to cool off throughout the day on Saturday, but there is still a lot of uncertainty surrounding the potential for persistent slab avalanches. Hedge your bets by sticking to conservative terrain.
Large cornices exist along ridgelines and require a wide berth from above and below. They have the potential to trigger slab avalanches from slopes below.
Two layers of concern exist and have been reactive over the past week. The upper layer is down 30-50 cm and consists primarily of a sugary facet interface. The deeper layer of concern is down 60-100 cm. This layer consists of surface hoar, faceted grains, and/or a melt-freeze crust. The layer has been most problematic around treeline elevations and in openings below treeline, but also reaches into the lower alpine.
Wet loose avalanches may still be possible on Saturday. The cooling trend is expected to be slow, with above freezing temperatures persisting for much of the day. Watch for signs of warming and snowpack instability such as rolling snowballs, moist snow and natural avalanche activity.
FRIDAY NIGHT - Mainly clear / moderate to strong southwest wind / alpine low temperature near 0 / freezing level 2500 m, dropping to 2000 m
SATURDAY - Mainly cloudy / moderate to strong southwest wind / alpine high temperature near -1 / freezing level 2000 m, dropping to 1500 m in the afternoon and to valley bottom overnight
SUNDAY - Mainly cloudy with isolated flurries, up to 5 cm / moderate to strong southwest wind / alpine high temperature near -5 / freezing level 1500 m, dropping to valley bottom overnight
MONDAY - A mix of sun and cloud / light west wind / alpine high temperature near -5 / freezing level 1500 m, dropping to valley bottom overnight
There is a lot of uncertainty with regard to how quickly temperatures will drop on Saturday, and how the persistent weak layers will respond to the cooling trend. Though often less of a concern than rapid warming, cooling in the wake of warm temperatures can also trigger a spike in avalanche activity.
On Friday, at the time of publishing, there were a few reports of human-triggered wet loose avalanches up to size 1.5, explosive triggered cornices up to size 1.5, and one explosive triggered size 2 persistent slab avalanche on a northeast aspect.
On Thursday, there were several reports of natural loose wet avalanches up to size 1.5 as well as natural and human-triggered wind and wet slab avalanches up to size 2. There were also a few reports of size 2.5 natural persistent slab avalanches in the nearby Waterton National Park region.
On Wednesday there were several reports of natural size 1 wet loose avalanches on solar aspects in the afternoon.
Warm temperatures and sunshine have made the snow surface moist in most areas. Dry snow may still be found on north aspects. The moist snow will change into a crust when temperatures finally dip back below zero. Wind slabs are likely still present on northerly aspects in the alpine and at treeline.
Up to 50 cm of snow sits above a variety of old interfaces that formed in mid-February. There is 60-100 cm sitting on a persistent weak layer that was buried in late January. These interfaces are mostly made up of sugary facets, hard wind pressed snow, surface hoar in wind-sheltered locations, and sun crust on steep solar aspects. Recent test results indicate that the late January persistent weak layer is potentially still quite reactive.
