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Avalanche Forecast

Archived

Feb 20th, 2019–Feb 21st, 2019

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

Regions

South Coast.

An unusual persistent weak layer makes steep and convex terrain features particularly dangerous at this time.

Confidence

High -

Weather Forecast

WEDNESDAY NIGHT: Clear skies and cold temperatures.THURSDAY: Dry, becoming cloudy. Freezing level around 600 m. Light northeasterly winds.FRIDAY: 10-15 cm new snow. Freezing level around 500 m. Moderate westerly winds.SATURDAY: 2-4 cm new snow, clearing. Freezing level around 500 m. Light southwesterly winds.

Avalanche Summary

On Monday, search and rescue responded to an avalanche in the Mount Seymour backcountry, which resulted in a fatality. The avalanche occurred on a steep feature at treeline elevation (see photo here). Avalanche professionals involved in the rescue indicated wide propagation consistent with a persistent slab problem. The crown depth was variable - 40 to 100 cm, indicating there was also wind loading in that area.On Friday and over the weekend, there is evidence of a widespread avalanche cycle up to size 2.5. These avalanches showed impressive propagation, with some being triggered remotely (from a distance) and some occasions stepping down to a 50 cm deep crust layer.

Snowpack Summary

40-80 cm of recent storm snow lies above a crust. The new snow has bonded poorly to this crust and natural and human-triggered avalanche have been noted on this interface. The reactivity of this layer appears to be worse in the south of the region (i.e. the North Shore Mountains) since this part of the region has seen more snow and it has consolidated into more of a slab. Unusually for this region, we expect this layer to remain reactive for some time into the future. New sun crusts may be found near the surface of south-facing aspects, while wind slabs may be found in exposed terrain. The lower snowpack is settled and strong.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.