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Avalanche Forecast

Archived

Dec 16th, 2019–Dec 19th, 2019

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

North Rockies.

Heavy snowfall and strong wind will create very dangerous avalanche conditions on Tuesday. Human triggered avalanches will remain likely the following days. 

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

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.

Avalanche Summary

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.

Snowpack Summary

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.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.