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Avalanche Forecast

Archived

Apr 12th, 2021–Apr 13th, 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 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

South Coast.

Sunny weather and warm temperatures will increase the likelihood of wet loose avalanches on sun-exposed slopes, and cornice failure. Expect to find pockets of wind slab at upper elevations, which may be reactive to human triggers.

Confidence

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

Weather Forecast

A ridge of high pressure, with sunny skies and high freezing levels will dominate the weather pattern this week.

Monday night - Mainly clear / moderate northeast wind / alpine low temperature near -5 / freezing level 1500 m 

Tuesday - Sunny / light to moderate northeast wind / alpine high temperature near -2 / freezing level 2000 m 

Wednesday - Sunny / moderate northeast wind / alpine high temperature near 4 / freezing level 2700 m 

Thursday - Sunny / light northeast wind / alpine high temperature near 4 / freezing level 2600 m

Avalanche Summary

There have been several size 1-2 natural and human triggered storm and wind slab avalanches reported over the past few days. These were mainly on northerly aspects in the alpine and at treeline. 

Looking forward, wind slabs are still possible to trigger at upper elevations, and wet-loose avalanches are expected with sun and warm temperatures. The likelihood of cornice failure also increases with warming.

Snowpack Summary

A storm late last week brought between 30-40 cm of new snow. The snow surface is now likely a crust in most areas, except on north aspects above about 1400 m where both soft snow and wind slabs may exist. In areas where the surface is a crust, sunshine and rising freezing levels are expected to soften the crust during the day.

Cornices are large and looming along ridgelines. Their release is unpredictable, requiring a large berth if you're travelling above or below them. Forecast rising freezing levels will increase the chances of cornice releases.

Terrain and Travel

  • Avoid sun exposed slopes, especially if snow surface is moist or wet.
  • Loose avalanches may start small but they can grow and push you into dangerous terrain.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.

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.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.