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Avalanche Forecast

Archived

Apr 13th, 2021–Apr 14th, 2021

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

Danger will progressively increase as the days get warmer and sunnier. Read more in this Forecasters' Blog.

Confidence

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

Weather Forecast

TUESDAY NIGHT: Clear skies, 40 km/h northeast wind, freezing level drops to valley bottom with treeline temperatures dropping to -7 C.

WEDNESDAY: Mix of sun and cloud, 40 km/h northeast wind, freezing level to 2000 m with treeline temperatures around -1 C.

THURSDAY: Sunny with a few clouds, light northeast wind, freezing level climbing to 2300 m with treeline temperatures reaching +1 C.

FRIDAY: Sunny, light northeast wind, freezing level climbing to 2500 m with treeline temperatures reaching +4 C.

Avalanche Summary

Recent reports are limited to a few small dry loose and wet loose avalanches on Sunday and Monday. Warm sunny weather this week will increase the size and likelihood of wet loose avalanches and cornice falls.   

Prolonged warming may increase the sensitivity of deeply buried layers later this week, although there is a fair bit of uncertainty about how likely this is in the South Rockies region. There have been some notable slab avalanches reported to the north of the region over the last few days including a skier triggered avalanche in Kananaskis Country on Saturday (see reports here and here) as well as a natural deep slab avalanche in Kootenay National Park on Tuesday (see photo here). These avalanches provide a good reminder of why it's good to be extra cautious during the heat of the day this time of year.

Snowpack Summary

North alpine terrain has roughly 30 cm of settling powder with wind slabs possible on steep exposed slopes. Other terrain is undergoing a melt-freeze cycle with successive days of warm sunny weather. The lower snowpack is generally strong and settled, however weak snow at the base of the snowpack 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

  • Avoid exposure to sunny slopes, especially in the afternoon.
  • Cornices become weak with daytime heating.
  • Loose avalanches may start small but they can grow and push you into dangerous terrain.
  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.

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.

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.