Avalanche Forecast

Issued: Mar 18th, 2019 4:11PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Loose Wet and Deep Persistent Slabs.

cgarritty, Avalanche Canada

South Rockies.

This is a good time to avoid avalanche terrain.

Summary

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 deepÂ 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

Sunshine and warm temperatures will peel away layers or recent snow on sunny slopes as loose wet slides, weaken cornices, and possibly re-energize wind slabs. Expect loose wet avalanche activity to expand to shaded aspects under sustained warming.

Be aware of overhead hazards and avoid exposure to avalanche runout zones.Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.Expect shaded aspects to become increasingly prone to loose wet avalanche activity.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 2.5

Deep Persistent Slabs

The weak layers present in our snowpack are undergoing a stress test that increases with each day of warm temperatures and weak overnight cooling. Deep weaknesses in the basal snowpack are especially concerning in thin snowpack areas in the alpine.

Sustained warming is testing deeply buried weak layers. Recognize and avoid overhead hazards.Buried surface hoar layers are a concern in sheltered openings like cutblocks at lower elevations.Thin snowpack areas in the alpine are becoming increasingly likely to produce deep persistent slabs.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 3

Valid until: Mar 19th, 2019 2:00PM