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Avalanche Forecast

Archived

Apr 12th, 2021–Apr 13th, 2021

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

Regions

South Rockies.

Watch for wind slabs lingering in steep open terrain and back off sun-exposed slopes as they heat up.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

MONDAY NIGHT: Mostly cloudy skies, 40-60 km/h northeast wind, freezing level drops to valley bottom with treeline temperatures dropping to -10 C.

TUESDAY: Mostly sunny, 40 km/h northeast wind, freezing level to 1500 m with treeline temperatures around -3 C.

WEDNESDAY: Mostly sunny, 30 km/h northeast wind, freezing level to 2000 m with treeline temperatures around 0 C.

THURSDAY: Mostly sunny, 30 km/h northeast wind, freezing level to 2200 m with treeline temperatures reach +2 C.

Avalanche Summary

A few small dry loose avalanches were reported on Sunday. There have been some notable slab avalanches reported to the north in Kananaskis Country and Banff over the last few days, including a near miss where a skier triggered a slab avalanche on Saturday that failed on a 70 cm deep facet layer. This avalanche occurred on a north aspect at 2100 m. See the MIN report here and a follow up by Kananaskis Public Safety here. 

Warming temperatures later this week could result in slab avalanches on old weak layers, however on Tuesday temperatures will remain relatively cool with the primary concerns being wind slabs, cornices, and wet loose avalanches.

Snowpack Summary

While sunny weather is melting the surface on southerly slopes, gusty northeast wind could blow around recent snow at upper elevations and form wind slabs on lee features. Upper elevations have 15-30 cm of settling snow from recent storm, but exact amounts are variable throughout the region due to the convective nature of the spring weather. The recent snow is sitting on hard crusts on solar aspects and a mix of wind affected or soft surfaces on shady aspects. 

The mid-pack is firm and well settled. Some faceted snow and a decomposing melt-freeze crust can be found near the base of the snowpack that may become a concern later this week when things really warm up.

The snow line is creeping up to higher elevations, so some common access points are now snow free.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid lee and cross-loaded terrain.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.