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Avalanche Forecast

Archived

Apr 18th, 2017–Apr 19th, 2017

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

Regions

Sea To Sky.

Wind slabs and cornices are the main concerns right now. Carefully assess terrain before committing to bigger lines.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

We're looking at unsettled and variably wet spring weather through Thursday, with clearing and fine weather for Friday.WEDNESDAY: More wet snow (5-15cm) above 1400m and the potential for intense squalls (and thunderstorms). Winds moderate southerly.THURSDAY: Isolated flurries (5-10cm) with wet snow above 1500m. Winds light southwesterly.FRIDAY: Sunny with cloudy periods. Freezing level rising to 2300m. High temperatures to +6 Celsius. Winds light southerly.NOTE: The convective flurries which are common during this time of year can result in widely varying snowfall amounts throughout a region. These spring squalls routinely drop 20+ cm of snow in one valley while the adjacent drainage remains dry. For this reason, the distribution of avalanche problems associated with new snow, such as wind slabs, can vary greatly within a region.

Avalanche Summary

On Tuesday we had reports of easily triggered soft slabs to Size 2 in the storm snow near Whistler. On Monday we had preliminary reports of an avalanche involvement in the Tantalus range near 2000m, aspect not known. All in the party got out safely.On Sunday, skiers triggered a Size 1.5 slab avalanche in a northwest facing couloir in the alpine near Whistler. See here for their MIN report. On Saturday, skiers triggered a Size 1.5 wind slab on the Spearhead traverse near Fissile, on a southwest aspect. See here for more details.

Snowpack Summary

On Monday into Tuesday we've had 10-15cm of fresh snow above 1400m. Southerly winds have created pockets of reactive wind slab (20-50cm thick) in the alpine and exposed features at treeline. Wind slabs have surprised skiers throughout the long weekend (see Avalanche Summary above). Warm temperatures on Sunday (+5 at treeline) and solar radiation resulted in a melt-freeze crust on south aspects at all elevations. The new snow is not expected to bond well to this crust and storm slabs may be more reactive on south aspects. Cornices remain large in some areas and could trigger large avalanches when they fail. The fatal accident near Lions Bay a week ago illustrates the danger of cornices breaking off, and the large avalanches they can trigger.

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.

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.