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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

Lizard-Flathead.

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 or 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 how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

SUNDAY NIGHT: Partly cloudy, light to moderate southwest wind, alpine low -2 C, freezing level dropping to 1700-1800 m. Potential for near freezing layer developing at surface.

MONDAY: Increasing cloud, flurries/light rain possible, 0-5 mm, light easterly wind, alpine high 0 C, freezing level 1800-2000 m. 

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

WEDNESDAY: Sunny, light south west wind, alpine high +2, freezing level 2200 m.

Avalanche Summary

A small (size 1) wind slab was triggered accidentally near Fernie on Saturday. The weekend also included reports of wet loose avalanches from size 1-2. On Thursday-Friday a few solar triggered slabs up to size 2 were noted.

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 north facing 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 50 cm of snow overlies a variety of old interfaces that formed in mid-February. There hasn't been recent avalanche activity on this layer, but it remains on the radar, especially in alpine terrain as things stay warm. The more active layer was buried late January, which is found 50 to 100 cm deep. This layer is mostly composed of sugary faceted grains or feathery surface hoar crystals. In specific terrain features the layer is still producing snowpack test results causing some concern for low probability high consequence avalanches, especially in this period of warming. 

Terrain and Travel

  • Be alert to conditions that change with aspect and elevation.
  • 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.
  • 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.