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Avalanche Forecast

Archived

Apr 20th, 2017–Apr 21st, 2017

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

Regions

Sea To Sky.

Warm temperatures and strong sunshine will combine to promote reactivity in a range of avalanche problems on Friday.

Confidence

Moderate -

Weather Forecast

Friday: A mix of sun and cloud. Light to moderate southeast winds. Freezing level to 2200 metres with alpine temperatures around 0 to +1.Saturday: Cloudy with flurries bringing 5 cm of new snow to higher elevations by evening. Moderate southeast winds. Freezing level dropping to 1700 metres over the day with alpine temperatures around 0 to -2.Sunday: Mainly cloudy with scattered flurries and a trace of new snow. LIght south winds. Freezing level to 1700 metres with alpine temperatures of -4.

Avalanche Summary

Reports from Wednesday include observations of explosives triggered storm slabs reaching Size 1.5 in the Whistler area. Crown depths averaged 20 cm.Very touchy conditions were reported in the Whistler backcountry on Tuesday, with skiers remote-triggering soft slab avalanches, running on the Easter crust. On Monday, a Size 2 avalanche was triggered on a west aspect in the Tantalus range near 2000m. See here for the excellent and informative MIN report.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.

Snowpack Summary

Stormy weather over the beginning of the week has brought about 30-40cm of new snow to the Sea to Sky mountains, with this precipitation falling as rain below about 1400m. Strong southeast winds over the same time period created pockets of reactive wind slab (up to 50 cm thick) in the alpine and exposed features at treeline, in addition to building fragile new cornice growth. A melt-freeze crust (the 'Easter crust') exists below this new snow on south aspects at all elevations. The new snow has begun to show signs of an improving bond with this crust. The mid and lower snowpack are generally well settled and strong.

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.