Avalanche Forecast

Issued: Feb 5th, 2018 4:53PM

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

jmcbride, Avalanche Canada

Northwest Inland.

New snow and wind build will continue to build reactive slabs especially in wind-exposed areas. Choose conservative terrain and minimize overhead exposure. Large avalanches have been observed in the past week.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Wednesday

Weather Forecast

TUESDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind light to moderate, southwest. Temperature -3. Freezing level valley bottom.WEDNESDAY: Snow. Accumulation 10-15 cm. Ridge wind light gusting to strong, southwest. Temperature -1. Freezing level 1000 m.THURSDAY: Mix of sun and cloud. Ridge wind light, east. Temperature -7. Freezing level valley bottom.

Avalanche Summary

Reports have been limited. On Saturday a small storm slab was reportedly human triggered on an east facing aspect around 1000 m. At the start of the storm on Wednesday and Thursday skiers triggered a few small slabs on steep convex rolls.There are no recent reports of persistent slab avalanche activity, but some notable large avalanches occurred 5-8 days ago. This includes some large (size 2-3) natural persistent slab avalanches in the Howsons, and two large (size 2.5) remotely triggered avalanches north of Kispiox. 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 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 formed in December are buried 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

Wind Slabs

Lingering windslabs remain a concern for human triggering especially on leeward slopes at higher elevations and near ridge crests. Watch for cracking and stiff or hollow feeling snow.

If triggered, storm slabs may step down to deeper layers resulting in large avalanches.Avoid lee and cross-loaded terrain near ridge crests or convex rolls.The recent snow may now be hiding windslabs that were easily visible before the snow fell.

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

Elevations: Alpine, Treeline.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Feb 6th, 2018 2:00PM