Snow likely to begin Monday and continues into Tuesday, but forecasters have low confidence in amount and timing. Heavier snowfall will elevate avalanche danger, while lighter amounts to a lesser degree.
Incoming warm temperatures, variable snowfall amounts, and persistent west winds will continue to build new wind slabs in the alpine and down to treeline on Monday.
Surface hoar buried January 3 sits 20–60 cm deep. Warming may help stiffen the overlying slab and increase reactivity where this layer exists. While not widespread, recent reports include small avalanches failing on this layer. Dig down and test for reactivity.
Basal facets remain near the ground. Red flags are fewer where the snowpack is deep, but on the eastern side of the forecast area, particularly in thin to thick snowpack transitions, the potential for deep slab avalanches remain.
Lake Louise reported triggering several size 1 wind slabs with explosives. Sunshine triggered a size 2 wind slab that also produced an adjacent size 1 in sympathy. During a flight to and from Lake Louise, Visitor Safety did not observe any new avalanches Sunday afternoon.
30-50 cm of recent storm snow with W-SW wind has formed windslabs. In sheltered areas below treeline, this new snow sits on a layer of surface hoar buried on Jan 3, but this layer is not widespread and more prominent on Hwy93S and in Yoho.
There is 50-90 cm over the Dec 15 melt-freeze crust, present to 1800-2000 m, and 100-200 cm over the November facet/crust interfaces. In thinner snowpack areas, facets are present at the base
Snow totals vary widely, with 10–50 cm possible depending on model guidance and location, and generally higher amounts expected in the west. Timing is most likely Monday into Tuesday. Temperatures will warm, with valley highs near +5 and alpine temperatures around −4. Strong, persistent southwest to west winds are expected. Taken together, this sharp combo will raise avalanche danger.
