Heavy snowfall and strong wind will create very dangerous avalanche conditions on Tuesday. Human triggered avalanches will remain likely the following days.
Large persistent slab avalanches are possible due to weak layers buried 30-50 cm below the surface. These layers of surface hoar, facets, and crusts have been reactive in recent snowpack tests and will become extra sensitive with the weight of the new snow. Conservative terrain choices are the best way to manage the uncertainties associated with this problem.
Steady snowfall and wind will create thick and reactive storm slabs this week. The most dangerous storm slab avalanches are expected with the intense snowfall on Tuesday, but steady snowfall and wind will keep them primed for human triggering for the rest of the week.
New snow will accumulate over the week with total accumulations of 30-60 cm between Monday and Thursday. The combination of heavy snowfall and strong wind will form new storm slabs across much of the region.
There is roughly 100-200 cm of snow on the ground around treeline elevations. The main layers of concern are currently buried 30-50 cm below the surface. These surface hoar and facet/crust layers formed in late November and have shown signs of being reactive in snowpack tests. These layers could become unstable with the weight of additional snow. Reports suggest they exist around treeline elevations throughout the region, and can likely be found in alpine terrain as well.
The lower snowpack contains several crust layers, which could be a concern in shallow areas along the eastern slopes of the region.
A week of stormy weather will bring moderate to heavy accumulations of snow and strong wind to the North Rockies.
MONDAY NIGHT: 10-15 cm of new snow to the McGregors/Kakwa/McBride area and 5 cm around Pine Pass and Tumbler Ridge, 50-80 km/h wind from the southwest, alpine temperatures around -8 C.
TUESDAY: Snow continues throughout the day with another 10-20 cm across the region, 60-100 km/h wind from the southwest, freezing level climbs to 1000 m, alpine high temperatures around -4 C.
WEDNESDAY: Scattered flurries with 5-15 cm of new snow, 40 km/h wind from the south, alpine high temperatures around -5 C.
THURSDAY: Another 5-15 cm of new snow then clearing in the afternoon, 40 km/h wind from the south, alpine high temperatures around -6 C.
Minimal avalanche activity has been reported in recent MIN reports. With heavy snowfall on the way, a cycle of natural storm slab avalanches will be likely at higher elevations during the peak of the storm on Tuesday. The storm snow will remain reactive to human triggering throughout the week, especially in areas that are continually being loaded by new snow and wind. There is more uncertainty about the likelihood of persistent slab avalanches, however any weak layers present in the snowpack will become more reactive with the weight of new snow.
