Avalanche Forecast

Issued: Mar 29th, 2018 4:05PM

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

mconlan, Avalanche Canada

Northwest Coastal.

New snow fell in the south of the region, which will produce new storm slabs and load buried weak layers. Conservative decision-making is recommended, as large avalanches are likely.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

THURSDAY NIGHT: Cloudy with snowfall, accumulation 5 to 10 cm, moderate southwesterly winds, alpine temperature -6 C, freezing level 500 m.FRIDAY: Mostly cloudy, light northwesterly winds, alpine temperature -5 C, freezing level 800 m.SATURDAY: Mostly cloudy, light southwesterly winds, alpine temperature -6 C, freezing level 700 m.SUNDAY: Mostly cloudy, light southwesterly winds, alpine temperature -7 C, freezing level 400 m.

Avalanche Summary

On Wednesday, large (size 2.5) persistent slab avalanches were reported in the region at alpine and treeline elevations, being remotely triggered (from a distance), 50 to 150 cm deep, and on northeasterly aspects. Similarly, large (size 2) storm slabs were explosively controlled near Terrace on easterly to northeasterly aspects, with slab depths of 40 to 75 cm, at elevations around 1200 to 1350 m. Loose dry avalanches were also explosively controlled on easterly aspects.On Tuesday, numerous large (size 2-3) persistent slabs released remotely on a layer of surface hoar buried 40-60 cm deep in the Terrace area. This activity was focused on shaded aspects at treeline and below treeline elevations.

Snowpack Summary

Thursday's storm is expected to bring another 10 to 30 cm of snow to the southern parts of the region. This overlies last weekends 50 to 80 cm of storm snow, with the highest accumulation at high elevations and closest to the coast. Strong westerly winds have redistributed last weeks snow in open areas.Two layers of surface hoar exist in the region at depths of about 40 to 60 cm, being buried early and mid-March. At low elevations, a melt-freeze crust also exists.Numerous dormant layers exist deeper in the snowpack. Layers of crusts, facets, and isolated surface hoar buried 50 to 100 cm exist from mid- and late-February. A surface hoar/crust layer from January is buried around 150 to 200 cm. Near the bottom of the snowpack, weak and sugary facets exist in colder and dryer parts of the region, such as the far north.

Problems

Persistent Slabs

A weak surface hoar layer buried about 50 cm has produced large slab avalanches that have propagated widely. It is best to avoid sheltered north to easterly slopes, where this layer is most likely to be a problem.

Use extra caution in open trees and sheltered features where surface hoar may be preserved.Be aware of the potential for large, destructive avalanches due to buried surface hoar.

Aspects: North, North East, East, South East.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 3

Storm Slabs

New snow fell in the south of the region, producing fresh slabs that overly previous storm and wind slabs. Observe for signs of instability, such as cracking, whumpfing, and avalanche activity.

If triggered, storm slabs may step down to deeper layers, resulting in large avalanches.Approach lee and cross-loaded slopes with caution.Be aware of the potential for loose dry avalanches in steep terrain where snow hasn't formed a slab.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Mar 30th, 2018 2:00PM