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Avalanche Forecast

Archived

Mar 12th, 2021–Mar 13th, 2021

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

Regions

South Rockies.

It's going to be a hot and sunny day! Temperatures are forecast to stay above freezing between 1500 m and 2500 m overnight. On Saturday, solar input and the freezing level rising to 2800 m will weaken cornices and may increase the reactivity of the persistent weak layers. 

Confidence

High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

FRIDAY NIGHT: Mostly clear, 15 km/h northwest wind, alpine low -9 C, above freezing layer between 1500 m and 2500 m.

SATURDAY: Sunny, 10 km/h south wind, alpine high +7 C, freezing level 2800 m.

SUNDAY: Sunny, 15 km/h south wind, alpine high +7 C, freezing level 2700 m.

MONDAY: Mix of sun and cloud, trace of new snow, 20 km/h northeast wind, alpine high +4 C, freezing level 2100 m.

Avalanche Summary

No new avalanches were reported for the area on Friday.

Snowpack Summary

A dusting of snow overlies a thick melt-freeze crust in many areas, with the exception being on north aspects above around 1700 m. Old wind slabs may exist on northerly aspects at alpine and treeline elevations, whereas windward slopes have been scoured to rocks or a hard crust. On solar aspects and below the freezing level, the snow may moisten during the heat of the day. Cornices may also weaken over the day.

Around 30 to 60 cm of snow sits above a persistent weak layer of sugary faceted grains that was buried in mid-February. There have been a handful of avalanches that released on this layer in the past few weeks. There is another persistent weak layer that was buried at the end of January, found around 50 to 80 cm deep. This layer consists of feathery surface hoar, facets, and/or a hard melt-freeze crust. Periodic avalanches continue to be triggered on these layers by riders, particularly where a stiff wind slab sits above them. Check out this MIN that shows the positioning of the layers in the snowpack near Crowsnest Pass.

Weak faceted snow and a decomposing melt-freeze crust can be found near the base of the snowpack. 

Terrain and Travel

  • Cornices become weak with daytime heating or solar exposure.
  • Cornices often break further back than expected; give them a wide berth when traveling on ridgetops.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
  • Be alert to conditions that change throughout the day.

Problems

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.