Avalanche Forecast

Issued: Nov 29th, 2017 4:40PM

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

jmcbride, Avalanche Canada

Northwest Coastal.

The recent stormy weather has dumped as much as 100 cm of new snow on last week's crust. This has created storm slabs and there have been reports of large natural avalanches. The new snow will take some time to settle.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

THURSDAY: Flurries, accumulation 5-10 cm, Moderate southwest wind. Alpine temperature -5. Freezing level 800 m.FRIDAY: Flurries, accumulation 10-15 cm, Moderate southwest wind. Alpine temperature -7. Freezing level 500 m.SATURDAY: Mix of sun and cloud. Light to moderate north west wind. Alpine temperature -7. Freezing level 300 m.

Avalanche Summary

Natural avalanche activity in the alpine to Size 2 was reported west of Kasiks on Tuesday morning. Also on Tuesday skiers in the Shames area reported "hearing a large avalanche" from a valley adjacent to the ski area. In recent days other observers in the Terrace area report shooting cracks within the recent storm snow (see the Mountain Information Network (MIN) post from Nov 25). Continued snow and wind are expected and the recent storm snow will take some time to settle. Travel in avalanche terrain will require very conservative route-finding and terrain choices. Please post your observations to the MIN.

Snowpack Summary

Recent stormy weather has brought about 90-130 cm of storm snow to the southern part of the region and now lies on the supportive 5-10 cm thick, November 23 rain crust from last week. Below this crust is a weak layer that formed in late October and is now buried 120-160 cm within the snowpack. Beneath this October crust is a 20-30 cm thick layer consisting of several thin crusts and facets. Recent snowpack tests report easy to moderate, sudden compression test results within the storm snow as well as moderate to hard, sudden results on the October 31 layer near the base of the snowpack.Across the southern part of the region snowpack depths average about 120 m at 800m elevation, and up to 180 cm at 1200 m. Reports from the north near Ningunsaw, describe a a much shallower snowpack. Here, a possible 30-40 cm of recent storm snow may now overlie a thin lower snowpack composed mainly of facetted snow. Snow depths in this part of the region range are from 60-120 cm between 600 and 1100 m elevation.

Problems

Storm Slabs

Storm snow is settling rapidly creating widespread storm slabs. These slabs will be most prominent above treeline where there has been additional loading from wind.

The new snow will require several days to settle and stabilize.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Deep Persistent Slabs

There have been no recent reports of avalanches on this layer however recent snowpack tests have produced hard, sudden results.

If triggered the storm slabs may step down to deeper layers resulting in very large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

3 - 4

Valid until: Nov 30th, 2017 2:00PM