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Avalanche Forecast

Archived

Apr 17th, 2017–Apr 18th, 2017

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

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 throughout the forecast period. TUESDAY: Wet snow Monday overnight through Tuesday (10-20cm by Tuesday afternoon). Freezing level around 1600 m. Winds moderate southwesterly.WEDNESDAY: More wet snow (10-15cm) above 1500m. Winds strong southerly.THURSDAY: Flurries continue (5-10cm) with snow above 1600m. Winds 20-30 km/h from the south.

Avalanche Summary

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

Late last week we had 20-30 cm of settling storm snow above 1500m. Pockets of reactive wind slab (5-40cm thick) can still be found in the alpine and exposed features at treeline - this has surprised skiers throughout the long weekend (see Avalanche Summary above). Warm temperatures on Sunday (+5 at treeline) resulted in a melt-freeze crust on most aspects and elevations at treeline and below. 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.