Avalanche Forecast

Issued: Jan 25th, 2018 4:31PM

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

jmcbride, Avalanche Canada

Northwest Inland.

Watch for areas where wind and storm snow have formed cohesive slabs above the recently buried crust/ surface hoar layer. A release near the surface may step down to a deeper layer.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Light flurries. Accumulation trace. Ridge wind light, southeast. Temperature -12. Freezing level valley bottom.FRIDAY: Cloudy, light flurries. Accumulation trace. Ridge wind light, southwest. Temperature -11. Freezing level valley bottom.SATURDAY: Mix of sun and cloud. Ridge wind light to moderate, east. Temperature -12. Freezing level valley bottom.SUNDAY: Snow. Accumulation 5-15cm. Ridge wind strong, southeast. Temperature -12. Freezing level valley bottom. Alpine inversion.

Avalanche Summary

On 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.On Monday there were reports from areas north of Kispiox of reactive storm slabs up to size 1.5 and 25 cm deep releasing with skier traffic on steeper, convex terrain.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 from 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 crusts and surface hoar layers that were buried late-December and mid-December and now lie 50-80 cm below the surface. Recent persistent slab activity over a surface hoar and facet 'combo' at low elevations suggests that a dangerous persistent slab problem may be developing as the mid and upper snowpack consolidate into a stiffer slab over this layer.

Problems

Storm Slabs

Recent storm snow has formed reactive slabs above the most recent crust/ surface hoar interface. Winds earlier in the week have also created pockets of wind slab in leeward areas in the alpine and at treeline.

Caution on steep slopes and convex rolls at where a crust/surface hoar layer has been buried.Be careful with wind loaded areas, especially near ridge crests and roll-overs.

Aspects: All aspects.

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 treeline and below.

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

Unlikely - Possible

Expected Size

1.5 - 3

Valid until: Jan 26th, 2018 2:00PM