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Avalanche Forecast

Archived

Jan 9th, 2019–Jan 11th, 2019

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

Regions

Vancouver Island.

Main concerns: Wind Slab, Loose Wet, Cornice Fall.

Travel & Terrain Advice

Avoid travel in avalanche terrain during the peak of the next storm system. Avoid wind loaded features and convex rolls, especially at ridge top. Give growing cornices a wide berth when travelling both above and below them.

Avalanche Summary

Widespread small human triggered loose dry avalanches observed on Tuesday afternoon. These avalanches were triggered from all sufficiently steep terrain at treeline and below treeline.

Snowpack Summary

A brief lull in the storm parade produced widespread surface hoar development on many aspects at all elevations Sunday and Monday. These weak feathery crystals formed on top of settling recent storm snow. With the incoming storm system, this weak layer of snow will be buried in sheltered terrain at all elevations. Below these layers, old storm snow is beginning to settle and bond well to adjacent layers which include a thick strong crust. Some weak sugary facet crystals have formed around this crust, but have not shown evidence of reactivity. With incoming snow load and rising freezing levels, a very large trigger on a large alpine feature could potentially awaken deeper instabilities and produce very large avalanches.

Snowpack Details

Surface: 20-40 cm of new low density storm snow. Upper: A thick crust and weak buried surface hoar layers. Mid: Settling old snow and some unreactive crusts. Lower: well settled.

Past Weather

Clear and calm conditions on Monday across the forecast region followed by the arrival of the next vigorous Pacific frontal system Tuesday morning. Outflow winds were strong from the NE veering to strong to extreme from the SE with the onset of precipitation. Approximately 20-30 cm of new low density snow fell through the day Tuesday and was transported into lee terrain by strong SE winds.

Weather Forecast

WEDNESDAY: 50-80 mm of precipitation with freezing levels rising to around 1600 m. Strong winds from the SE. THURSDAY: 30-60 mm of precipitation with freezing levels around 1500 m. Strong winds from the SE. FRIDAY: 10-15 mm of precipitation with freezing levels around 1650 m. Winds strong easing to moderate from the SE.

Confidence

Moderate - Uncertainty in precipitation intensity and freezing levels.

Problems

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.

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.