Avalanche Forecast

Issued: Jan 29th, 2019 4:47PM

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

kdevine, Avalanche Canada

Northwest Coastal.

Persistent slabs may be reactive to human triggers, especially in lee areas. Conditions are highly variable from north to south within the region. In the southern portion of the region near Terrace and Kitimat, the hazard at treeline is likely low.

Summary

Confidence

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

Weather Forecast

TUESDAY NIGHT - Cloudy with flurries, up to 5 cm / southwest winds, 20-50 km/h / alpine low temperature near -4WEDNESDAY - Cloudy with flurries, up to 5 cm / southwest winds 20-40 km/h / alpine high temperature near -2THURSDAY - Snow, 10-20 cm / southwest winds 20-40 km/h / alpine high temperature near -2 FRIDAY - Flurries, 5-10 cm / southwest winds, 20-50 km/h / alpine high temperature near -2

Avalanche Summary

One natural size 2.5 avalanche was reported on Monday. It was a cornice failure that triggered a slab avalanche on a north aspect in an area close to Terrace.A widespread natural avalanche cycle to size 3.5 was reported on all aspects north of Stewart on Sunday. There were also two human triggered avalanches reported in this area on Sunday, one size 2 and one 2.5. These occurred on southerly aspects between 1500-1800 m.Another notable avalanche from near Stewart on Sunday was a human triggered size 3 that occurred on a northeast aspect at 2000m. This avalanche was triggered on a surface hoar layer that is buried approximately 100 cm in that location. This persistent weak layer was reportedly triggered from a shallow snowpack area. The avalanche was 500 m wide and ran on relatively moderate angled terrain.In the south of the region, closer to Terrace, there were reports of a natural avalanche cycle to size 3 in high alpine terrain on Sunday.

Snowpack Summary

Up to 40 cm of snow fell in the region on the weekend. The highest snowfall amounts were north of Stewart and tapered significantly to the south.This snow sits on a weak layer of surface hoar (feathery crystals), and a crust on sun-exposed slopes. The recent precipitation fell mainly as rain below about 1200 m in the north and below about 1600 m in the south.In some areas, there is another layer of surface hoar that is now buried 50-100 cm. A weak layer of facets (sugary snow) buried in early December exists down 180-250 cm.Avalanches triggered within the new snow have the potential to step down to these deeper layers, resulting in very large avalanches.

Problems

Persistent Slabs

There are a few layers of surface hoar in the top 100 cm of the snowpack. The most likely one for humans to trigger is the one that is buried up to 40 cm. This problem is most pronounced in the north but may exist at upper elevations in the south.

Watch for signs of instability such as whumpfing, or cracking, or recent avalanches.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.If triggered, smaller slabs may step down to deeper layers resulting in very large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Valid until: Jan 30th, 2019 2:00PM