Avalanche Canada ahanna, Avalanche Canada

South Rockies Avalanche Forecast

Mar 21st, 2020 4:00PM

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

Clouds may temper day-time warming. Minimize exposure to cornices and steep slopes that face the sun during the warmest part of the day. A deep weak layer remain a concern.

Summary

Confidence

High -

Weather Forecast

Saturday night: Partly cloudy with brief flurries bringing a trace. Light northwest wind. Freezing level valley bottom.

Sunday: Mix of sun and cloud. Moderate to strong southwest wind. Freezing level 1700 m.

Monday: Scattered flurries bringing trace. Moderate to strong southwest wind. Freezing level 1800 m.

Tuesday: 10-20 cm new snow. Light southwest wind. Freezing level 1000 m.

Avalanche Summary

A single snowmobile triggered size 1 wind slab was observed amid extensive slope "testing" on Friday. In neighboring Waterton National Park, solar-triggered loose dry and wind slabs up to size 1.5 were observed Thursday and Friday, having run surprisingly far on a crust. A size 2 deep persistent slab out of steep, thin, rocky alpine terrain Thursday reminds us that the basal facets still exist and can be triggered in this type of terrain. 

If you decide to travel in the backcountry, consider sharing your observations with us and fellow recreationists via the Mountain Information Network (MIN) to supplement our data stream as operators are shutting down. Even just a photo of what the day looked like would be helpful.

Snowpack Summary

Sunny skies have formed a melt-freeze crust on sun-exposed slopes. The alpine consists of wind affected snow from easterly wind, so you may find small pockets of wind slabs in atypical terrain features on south to west aspects.

A layer of faceted grains overly a melt-freeze crust from early February. This layer currently sits 40 to 80 cm below the surface. 

The base of the snowpack contains basal facets that are most prominent in shallow, rocky start zones.

Terrain and Travel

  • Carefully evaluate steep lines for wind slabs.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Rocks will heat up with daytime warming and may become trigger points for loose wet avalanches
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

Problems

Loose Wet

An icon showing Loose Wet

Likelihood

Unlikely-Possible

Expected Size

1 - 2

Modest air temperature and sunny skies combine to weaken the snow surface. As this occurs, loose wet avalanche activity may result. The highest likelihood of this occurring is during the heat of the day on sun-exposed slopes. Note that the same warming trend also weakens cornices, so best to stay well back from them on ridges and avoid travelling beneath them.

Aspects:

South East, South, South West.

Elevations:

All elevations.

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

Likelihood

Unlikely-Possible

Expected Size

2.5 - 3.5

Weak snow at the bottom of the snowpack hasn't gone away. Evidence of deep persistent slab avalanches has been focused in the Sparwood-Elkford area over the past month. Human triggering is most likely around steep, rocky terrain features or anywhere the snowpack is thin and weak. A failing cornice could initiate a deep persistent slab when it impacts the slope below.

Aspects:

All aspects.

Elevations:

Alpine, Treeline.

Valid until: Mar 22nd, 2020 5:00PM