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Avalanche Forecast

Archived

Mar 13th, 2021–Mar 14th, 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.

Regions

Kootenay Boundary.

Warm air and solar input are mainly driving the danger. The likelihood of triggering cornices and loose wet avalanches will increase over the day and there is uncertainty as to whether deeper weak layers could reactivate during this diurnal cycle period.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

SATURDAY NIGHT: Clear skies, 20 to 30 km/h south wind, alpine temperature 0 C, freezing level 2300 m but cooling at lower elevations.

SUNDAY: Sunny with increasing afternoon cloud, 20 to 30 km/h south wind, alpine temperature 0 C, freezing level 2200 m.

MONDAY: Mix of sun and cloud, 10 km/h northeast wind, alpine temperature 0 C, freezing level 2100 m.

TUESDAY: Mix of sun and cloud, 10 km/h northwest wind, alpine temperature 0 C, freezing level 2100 m.

Avalanche Summary

Small wind slabs were triggered naturally and by skiers on Friday out of steep northerly alpine terrain.

A relatively high freezing level and sunny periods may weaken the snowpack in the coming days and increase the likelihood of loose wet avalanches, cornice failures, and perhaps a reactivation of deeper weak layers.

Snowpack Summary

We are in the midst of a melt-freeze cycle, with freezing levels heightening above 2000 m. The snow surface is expected to freeze during the night and heat up during the day, particularly on southerly aspects during sunny periods. Dry snow may still be found at high elevations on north aspects. An overall weakening trend of cornices is expected during this diurnal cycle.

Deeper in the snowpack, a persistent weak layer from late January is buried around 80 to 150 cm and is composed of a combination of surface hoar, facets, and crusts. There is uncertainty about whether this problem will reactive during this diurnal cycle, but it remains possible. 

As always, best to avoid shallow, rocky areas where a weak and faceted snowpack may be found.

Terrain and Travel

  • Minimize your exposure time below cornices.
  • Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

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.

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.

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.