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Avalanche Forecast

Archived

Mar 19th, 2023–Mar 20th, 2023

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Rockies, St. Mary, Bull, Elkford East, Elkford West.

Use caution when transitioning into wind-affected terrain.

Stick to thick snowpack areas where you are less likely to trigger deep weak layers.

Confidence

High

Avalanche Summary

On Friday afternoon, a snowmobile triggered a large persistent slab avalanche (size 2.5) in the south Purcells. The avalanche occurred in burnt forested terrain on a south aspect at 2200 m. It failed on a 50 to 100 cm deep layer that is suspected to be a sun crust buried in February.

On Thursday in the Elk Valley, several size 3 wind slab avalanches were reported. They were triggered naturally and with the use of explosives. They stepped down to a deeply buried weak layer of facets. These avalanches were triggered at the upper end of treeline and in the alpine and were mostly in cross-loaded terrain features on west and northwest aspects.

On Wednesday, a skier accidental size 2 wind slab avalanche was triggered near St. Mary's. The avalanche occurred on a northeast aspect at treeline and stepped down to the basal facets. For photos and details check out the MIN report.

Snowpack Summary

Above 1400 m there is 20 to 40 cm of wind-affected snow that fell last week. It sits on a thin sun crust on solar slopes and wind-affected snow in open areas. A sun crust is found on the surface of solar slopes at all elevations.

In the Purcells around St Mary's, several weak layers from January and February can be found down 50 to 120 cm. The mid-snowpack is generally well-settled.

The lower snowpack is made up of a widespread layer of large, weak basal facets and depth hoar in some areas. This weakness has been responsible for a number of recent very large, destructive avalanches and will continue to be a concern.

Weather Summary

Sunday Night

Mostly cloudy with clear periods, no accumulation, winds southeast 10 km/h, treeline temperatures -5 to 0 °C.

Monday

Cloudy with sunny periods, no accumulation, winds east 15 km/h, freezing levels 1700 m.

Tuesday

A mix of sun and cloud, no accumulation, winds east northeast 20 km/h, freezing levels 1000 to 1500 m.

Wednesday

Sunny with cloudy periods, no accumulation, winds northwest 20 km/h, freezing levels up to 2000 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
  • Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

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.