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Avalanche Forecast

Archived

Mar 14th, 2021–Mar 15th, 2021

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

Regions

South Rockies.

Less solar input is expected on Monday, but some elevation bands may not get a good overnight re-freeze. Move off slopes before they get wet and slushy. Consecutive days in a row of warm temperatures may increase the reactivity of deeper weak layers and cornices.

Confidence

Moderate - Uncertainty is due to difficult to forecast freezing levels. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

SUNDAY NIGHT: Partly cloudy, light to moderate west wind, alpine low -2 C, freezing level dropping to 1700-1800 m in the am, potential for near freezing layer at surface overnight.

MONDAY: Increasing cloud, flurries/light rain possible, 0-5mm, light easterly wind, alpine high 0 C, freezing level 1900-2000 m.

TUESDAY: Mostly sunny, light to moderate west wind, alpine high +2 C, freezing level 2200 m.

WEDNESDAY: Mostly sunny, light to moderate southerly wind, alpine high +2, freezing level 2200 m.

Avalanche Summary

There were wet loose avalanches size 1.5-2 from south and west facing alpine terrain reported in the South Rockies on Saturday.

Snowpack Summary

Wind slabs in the alpine may linger, especially on northerly aspects. Snow on all solar aspects and elevation bands has been getting moist by mid morning and may not be getting a good overnight re-freeze of late. Snow on northerly terrain above 1500 m has so far remained dry, but this could change on Monday depending on the snow rain line and freezing levels. Cornices are large and looming, and glide cracks are increasing in size...both should be considered unpredictable and given a wide berth.

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

  • Be alert to conditions that change with aspect and elevation.
  • Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.
  • Cornices become weak with daytime heating or solar exposure.
  • Be alert to conditions that change throughout the day.

Problems

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.

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.