Avalanche Forecast

Issued: Feb 8th, 2018 4:54PM

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

Avalanche Canada jmcbride, Avalanche Canada

Natural activity will likely taper off on Friday, however expect the new storm slabs to remain primed for human triggering especially in wind-loaded areas.  Choose conservative terrain and be aware of overhead hazard especially on sunny aspects.

Summary

Confidence

Moderate - Freezing levels are uncertain on Saturday

Weather Forecast

FRIDAY: Mostly sunny. Ridge wind light to moderate, northeast. Temperature -10. Freezing level valley bottom.SATURDAY: Mostly sunny. Ridge wind light, southwest. Temperature near 0. Freezing level 1600 m.SUNDAY: Mostly sunny. Ridge wind light, north. Temperature -6. Freezing level valley bottom.

Avalanche Summary

A widespread natural avalanche cycle occurred in the Terrace and Shames areas during Wednesday's storm with reports of numerous storm slab avalanches up to size 2 running far and fast in the new snow at all elevations.Tuesday there were reports of two skier triggered size 1 wind slab releases just northwest of Terrace, where a soft slab up to 35 cm deep had formed on wind-loaded features.Monday evidence of a natural avalanche cycle from size 2.5 - 3.5 was reported on north to south aspects between 1000-1700 m, west of Terrace, with several persistent slabs suspected to have failed on the mid or early January layers during the height of the weekend's storm.On the weekend persistent slab activity was reported north of Meziadin Junction where a natural size 4 and a natural size 3.5 were observed on a southwest and northeast aspect at 1800-2000 m and are suspected to have failed on the mid-January layer.

Snowpack Summary

Wednesday's storm delivered another 30-50 cm of new snow, and a mix of rain and freezing rain for areas west of Terrace, bringing storm snow totals of over 100 cm in the last 10 or 12 days for the Terrace area. Northern areas have seen about 50-70 cm of recent storm snow.Beneath the storm snow lies a 5-20 cm thick crust that was buried early February and can be found 60-110 cm below the surface on all aspects up to 1400 m. A weak layer buried in mid-January is 120-150 cm below the surface and remains a concern. In most areas this layer is a crust, but it may also be surface hoar in sheltered areas at treeline and below. This layer produced a few human triggered avalanches throughout the region over the past week, and may remain reactive as it adjusts to the weight of the new snow.In thinner snowpack areas (north and inland), deeper crust / surface hoar layers that were buried in December and early January may still be a concern as well. They are buried over 150 cm below the surface, but may still be triggerable from shallow spots.

Problems

Storm Slabs

An icon showing Storm Slabs
Wednesday's storm event has formed reactive storm slabs at all elevations but especially in wind-exposed areas at treeline and above. Be aware that these slabs overlie a crust from early-February and may also step down to a deeper weak layer.
Be careful with wind loaded areas, especially near ridge crests and roll-overs.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs
A weak layer exists 120-150 cm below the surface. It may still be possible for humans to trigger persistent slab avalanches on this layer, or for a storm slab release to step down to this layer resulting in a very large avalanche.
Caution around convexities or areas with a thin or variable snowpack.Minimize overhead exposure during periods of heavy loading from new snow, wind.Avoid lingering in runout zones. Large avalanches may run long distances.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2.5 - 4

Valid until: Feb 9th, 2018 2:00PM