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Avalanche Forecast

Archived

Apr 14th, 2021–Apr 16th, 2021

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

Regions

North Rockies.

Avalanche danger will increase throughout the day due to warm sunny weather. 

Plan on finishing early and minimizing your exposure to overhead avalanche terrain. Read more in this Forecasters' Blog.

 

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

WEDNESDAY NIGHT: Clear skies, light east wind, alpine temperatures stay slightly above freezing with sub-zero temperatures in the valleys.

THURSDAY: Clear skies, light southeast wind, freezing level reaching 3000 m and treeline temperatures reach +7 C.

FRIDAY: Clear skies, light wind, alpine temperature 5 C, freezing level steady at 3000 m and treeline temperatures around+7 C.

SATURDAY: Clear skies with some high clouds in the afternoon, light west wind, freezing level around 2500 m and treeline temperatures around +5 C.

Avalanche Summary

Natural avalanche activity has been reported on sun-exposed slopes over the last few days, including an impressive photo in this MIN report from Kakwa on Tuesday. Most activity has been relatively small (size 1-1.5) wet loose avalanches, but they will likely get bigger when it gets warmer on Thursday and Friday. A few wind slab avalanches (up to size 2.5) were reported over the weekend, but this problem has likely settled down since then. There have been some large deep persistent slab avalanches triggered by warming to the south around Jasper and Banff, but we are uncertain whether this problem will extend into the North Rockies.

Looking forward, warm sunny weather will drive avalanche danger with wet loose avalanches likely and the possibility for deep persistent slab avalanches in some areas. These problems are best managed by minimizing your exposure to avalanche terrain when it gets warm.

Snowpack Summary

Warm temperatures are melting the surface on all but the highest north-facing slopes, creating weak surface snow during the heat of the day. Crusts may form overnight. Large cornices hang above many ridgelines and will also weaken with the warming.

As heat penetrates deeper into the snowpack it has the potential to reactivate deeper weak layers, including a layer from mid-February and basal layers. The most likely areas to be concerned about deeper weak layers are shallow parts of the region along the eastern slopes of the Rockies like Core Lodge, Wolverine, Bullmoose, Upper Burnt and perhaps around Mt. Robson.

Terrain and Travel

  • Avoid exposure to sunny slopes, especially in the afternoon.
  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.

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.

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.

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.