Avalanche Forecast

Issued: Feb 6th, 2018 4:46PM

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

jmcbride, Avalanche Canada

Northwest Inland.

New snow and wind will load several buried weak layers in the snowpack. Choose conservative terrain and minimize exposure to overhead hazard. Large avalanches may run long distances.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

TONIGHT: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind moderate, west. Temperature -4. Freezing level valley bottom.WEDNESDAY: Snow. Accumulation 10-15 cm. Ridge wind light to moderate, southwest. Temperature -6. Freezing level valley bottom.THURSDAY: Mostly cloudy, light flurries. Accumulation trace. Ridge wind light, northeast. Temperature -12. Freezing level valley bottom.FRIDAY: Sunny. Ridge wind light, northeast. Temperature -12. Freezing level valley bottom.

Avalanche Summary

On Monday evidence of a natural avalanche cycle from size 1.5-2.5 was reported on north through south aspects between 1200-1600 m in the Howson Range failing both in the recent storm snow as well as the deeper mid-December layer. A natural size 2.5 that failed on a deep weak layer of sugary, facets at the base of the snowpack was also reported from the northern part of the region near Ningunsaw.On Saturday a small storm slab was reportedly human triggered on an east facing aspect around 1000 m. And at the start of the storm on Wednesday and Thursday skiers triggered a few small slabs on steep convex rolls.Last week some large (size 2-3) natural persistent slab avalanches in the Howsons, and two large (size 2.5) remotely triggered avalanches north of Kispiox were reported. We have no information from the Smithers area, but suspect a similar deeper weakness could exist there too. Activity on buried weak layers is most suspect during periods of heavy loading or rapid warming, hence it's time to be cautious.

Snowpack Summary

Approximately 30-50 cm of storm snow has accumulated since last Thursday. The snow has mostly fallen as low density powder, but may have settled in some areas that experience a brief period of warming on Friday. A crust and/or weak feathery surface hoar layer buried in mid-January now lies 60-100 cm below the surface. The crust exists well into the alpine and the surface hoar can be found in sheltered areas in the lower alpine and treeline elevations. Another two crust / surface hoar layers that were buried in December are now 80-120 cm below the surface. These layers produced sudden results in recent snowpack tests and have been the suspected weak layer in recent large remotely (from a distance) triggered avalanches.

Problems

Storm Slabs

New snow and wind will form new storm slabs particularly at upper elevations and in wind-exposed areas. These slabs may be reactive to human triggering and a release may have the potential to step-down to a deeper layer buried in the snowpack.

Avoid lee and cross-loaded terrain near ridge crests or convex rolls.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

There is limited information about weak layers buried 60-100 cm below the surface. They produced a few large avalanches last week, and may remain sensitive to human triggering in shallow snowpack areas.

Avoid lingering in runout zones, avalanches triggered up high may run long distances.Avoid shallow or thick to thin snowpack areas where triggering a deeper layer is more likely.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3.5

Valid until: Feb 7th, 2018 2:00PM