Avalanche Forecast

Issued: Mar 19th, 2017 3:31PM

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

cgarritty, Avalanche Canada

Northwest Inland.

Recent shifting winds have been driving a wind slab problem at higher elevations. Slabs have proven especially touchy where they overlie a recent rain crust.

Summary

Confidence

High -

Weather Forecast

Monday: A mix of sun and cloud. Light to moderate southeast winds. Freezing level to 900 metres with alpine temperatures of -7. Tuesday: Cloudy with sunny periods and flurries beginning in the afternoon. Light southeast winds. Freezing level to 1000 metres with alpine temperatures of -3. Wednesday: Mainly cloudy with scattered flurries bringing a trace to 5 cm of new snow. Moderate to strong southeast winds. Freezing level to 1100 metres with alpine temperatures of -2.

Avalanche Summary

Reports from Saturday include observations of a natural avalanche cycle in the Howson Range, where several Size 2.5-3.5 storm slabs released naturally from north to east aspects between 1200-1700 metres. A MIN report from the Telkwa area also details a snowmobile triggered Size 2.5 wind slab. The March 14 crust mentioned in our snowpack discussion was identified as the failure plane in this occurrence as well as in a skier triggered Size 2 wind slab north of Kispiox. These close calls should draw attention to the extent of recent wind transport as well as the March 14 crust's excellent performance as a sliding layer.

Snowpack Summary

At treeline and above, ongoing winds have been redistributing recent storm snow and light new snow amounts into wind slabs in lee terrain. New snow amounts taper with elevation and lie over a supportive crust (March 14) at about 1300 metres and below. This crust has been observed at higher elevations in the Telkwa area, and wind slabs have proven especially reactive where they sit above it. At higher elevations, wind redistribution is incrementally loading a weak interface that was buried in late February. The interface is composed of facets, crusts, and surface hoar and may be 40-60 cm deep. There's still some uncertainty around the distribution and reactivity of this interface, but it has proven reactive under skier traffic in the north of the region. The mid-pack is well consolidated, but sits above weak, sugary snow near the ground. This deep basal weakness remains an ongoing concern in thin rocky start zones and in shallow snowpack locations.

Problems

Wind Slabs

Recent winds have been shifting between a variety of directions and are set to do so again on Monday. Expect to find wind slabs on a range of aspects as you gain elevation and be aware of a recently formed rain crust acting as a touchy sliding layer.

Be increasingly cautious as you transition into wind affected terrain.Be alert to conditions that change with elevation and aspect.If triggered, wind slabs may step down to deeper layers and result in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Deep Persistent Slabs

Even if it isn't making regular appearances, the lingering weakness at the bottom of our snowpack is here to stay. This layer will be most reactive in thin rocky start zones and in shallow snowpack locations.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Mar 20th, 2017 2:00PM