Avalanche Forecast

Issued: Jan 27th, 2018 4:46PM

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

jmcbride, Avalanche Canada

Northwest Inland.

Wind and storm snow have formed cohesive slabs above the recently buried crust/ surface hoar layer at upper elevations. It may also be possible to trigger a buried weak layer from thin snowpack areas.

Summary

Confidence

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

Weather Forecast

TONIGHT: Increasing cloud. Ridge wind light, southeast. Temperature -15. Freezing level valley bottom.SUNDAY: Cloudy, flurries. Accumulation 2-5 cm. Ridge wind strong, southeast. Temperature -12. Freezing level valley bottom. Alpine Inversion.MONDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind strong, southwest. Temperature -8. Freezing level 200 m.TUESDAY: Cloudy, flurries. Accumulation 2-5 cm. Ridge wind moderate, southwest. Temperature -10. Freezing level valley bottom.

Avalanche Summary

Friday there was a report of a helicopter remotely triggering a Size 2.5 wind slab from above the slope on a west aspect at 1500 m north of Kispiox.Thursday there was a report of skiers, north of Kispiox, remotely triggering a Size 2-2.5 avalanche from a safe location on a ridge that released on the adjacent slope on a northwest aspect at 1650 m. A weak layer buried late-December was the suspected failure plane.Wednesday there was a report of a skier-triggered Size 1 wind slab avalanche on a northwesterly aspect at 1650 m in the northern part of the region, east of Ningunsaw.Tuesday there were reports of easily-triggered wind slabs 30-40 cm deep releasing to Size 1 in wind-loaded areas near ridge crests in the alpine in the southern part of the region.Reports from late last week showed a notable increase in persistent slab activity at lower elevations in the Howson Range. In this area, three Size 2 releases failed on steeper terrain with remote triggers on the mid-December weak layer, found 50 cm below the surface.

Snowpack Summary

Recent light snowfalls have gradually brought 20-60 cm of new snow across the region. This new snow has buried the mid-January interface which features a crust that exists well into the alpine and isolated pockets of surface hoar in sheltered areas at lower alpine and treeline elevations. Below the mid-January interface, deeper weak layers in the snowpack include two separate crust and surface hoar layers that were buried late-December and mid-December and now lie 50-80 cm below the surface. In the past week these deeper layers have produced hard but sudden results in recent snowpack tests as well as recent large avalanches triggered from a distance.

Problems

Wind Slabs

Wind slabs can be found on leeward aspects in the alpine as well as wind-exposed areas at treeline. These slabs overly a thin crust/ surface hoar layer and have been reactive to light triggers especially in steep or convex terrain near ridge crests.

Be careful with wind loaded areas, especially near ridge crests and roll-overs.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

Weak layers buried in the snowpack have produced recent avalanches with very light triggers particularly on unsupported features at lower elevations.

Watch for signs of instability such as whumpfing, or cracking at lower elevations.Avoid shallow or thick to thin snowpack areas where triggering a deeper layer is more likely.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 3

Valid until: Jan 28th, 2018 2:00PM