Avalanche Forecast

Issued: Feb 20th, 2019 4:04PM

The alpine rating is moderate, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Persistent Slabs and Wind Slabs.

jfloyer, Avalanche Canada

South Coast.

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

Summary

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

There is a weak layer of facets over a crust buried approximately 50 cm below the surface. Persistent slab problems are unusual for this region. Cautious terrain selection is needed to remain safe.

Be aware of the potential for wide propagations due to the presence of a buried weak layer.Avoid travel on steep slopes and convex rolls.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Likely

Expected Size

1.5 - 2.5

Wind Slabs

30-50 cm of recent storm snow may be poorly bonded to crusts.

Use caution above cliffs and terrain traps where small avalanches may have severe consequences.Use caution on open slopes and convex rolls The new snow may require several days to settle and stabilize.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Feb 21st, 2019 2:00PM