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Avalanche Forecast

Archived

Mar 18th, 2019–Mar 19th, 2019

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

Regions

South Rockies.

This is a good time to avoid avalanche terrain.

Confidence

Moderate -

Weather Forecast

Monday night: Mainly clear. Light north winds. Freezing levels rising from 2700 to 3000 metres.Tuesday: Sunny. Light variable winds. Alpine high temperatures around +6 with freezing levels rising to 3200 metres and remaining elevated overnight.Wednesday: Sunny. Light southeast winds. Alpine high temperatures around +7 with freezing levels around 3200 metres, dropping slightly overnight. Thursday: Mainly sunny. Light southwest winds. Alpine high temperatures around +6 with freezing levels around 3000 metres, dropping slightly overnight.

Avalanche Summary

A report from Sunday in the Window Mountain area described snowshoeing party choosing to turn back after avoiding a large loose wet avalanche that ran into below treeline terrain. This highlights the importance of considering overhead hazards being warmed by the sun and potentially inverted (warmer at higher elevations) temperatures.On Thursday, a group of riders remotely triggered a size 1.5 persistent slab from 100 metres away. See the MIN report for details. I view this as an important piece of data when considering the effect of forecast strong sunshine and warming.Saturday's reports showed initial warming producing only small loose wet avalanches. Neighbouring regions (for example Kananaskis Country) where the snowpack is thinner and weaker entered a natural avalanche cycle involving most aspects, most elevations, and most snowpack layers. Concern is increasing for deep basal snowpack weaknesses that have the potential to produce very large and destructive avalanches.

Snowpack Summary

Upper snowpack: Getting warm and moist during the day, maybe forming weak crusts overnight that deteriorate during the day. On sunny aspects there may be buried crusts serving as sliding layers. On lee slopes there may be buried hard layers of wind effected snow (buried wind slabs).Mid pack: The mid-snowpack consists of sugary faceted grains (facets) and layers of harder wind effected snow. In isolated wind protected locations a thin surface hoar layer from mid-January is 50-80 cm deep. The surface hoar is most prominent in the Elk Valley between 1600 - 1900 m. See Avalanche Activity section below for why this is relevant.Lower pack: The strength of the lower snowpack is is very much in question in shallower areas where the February cold was able to penetrate and weaken basal layers.Forecasting how many sunny days and warm nights it's going to take to wake up deeper layers is tough, but we can say with confidence that it's a good time to stand aside and let the mountains shed their coat. Stability will improve greatly when temperatures cool off.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.