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 on the slopes below.
Two layers of concern exist and have been reactive over the past week. The upper layer is down 30-60 cm and consists primarily of a sugary facet interface. The next layer is down 60-100 cm and consists of surface hoar, facets, 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 -1 / 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 - Cloudy with sunny periods and isolated flurries / 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 / moderate west wind / alpine high temperature near -6 / 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 Thursday, there were several reports of natural and human-triggered wet loose avalanches up to size 1.5. There was also a few size 2 solar triggered wind slab avalanches reported on south to southeast aspects. In addition, there were three size 2.5 natural persistent slab avalanches reported in the nearby Waterton National Park region.
There were a few size 1 natural and human-triggered wet loose avalanches reported on solar aspects on Wednesday. There were also reports of several size 2-2.5 natural wet loose avalanches in the neighbouring Waterton National Park region, and two size 2.5 natural persistent slab avalanches in the neighbouring Kananaskis Country region.
Warm temperatures and sunshine have made the snow surface moist in most areas. Dry snow may still be found on north aspects. This moist snow will change into a crust when temperatures finally dip back below zero. Wind slabs are likely still present on north to east aspects in the alpine and at treeline. Upper elevations have been scoured down to rocks or crusts in many areas due to recent strong southwest winds.
40-60 cm (in some places up to 100 cm) of snow sits above a persistent weak layer of facets that was buried in mid-February. Recent snowpack tests indicate that this layer is reactive and has the potential to propagate widely, causing large avalanches.
There is another persistent weak layer that was buried at the end of January. This layer consists of surface hoar, facets, and/or a hard melt-freeze crust. recent MIN reports show that these layers remain easily triggered by people.
Weak faceted snow and a decomposing melt-freeze crust can be found near the base of the snowpack.
