Avalanche Forecast

Issued: Dec 28th, 2016 3:56PM

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

jfloyer, Avalanche Canada

Northwest Coastal.

Significant accumulations of new snow will remain touchy, particularly in wind drifted areas, or in sheltered areas where it overlies a weak snowpack layer.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

THURSDAY: Light snow 5-10 cm, winds around 40 km/h from the southeast. Treeline temperatures around -7C.FRIDAY: Mix of sun and cloud, 40-60 km/h northwest winds, temperatures around -8C in the south of the region, colder further north.SATURDAY: An overnight storm may put up to 10 cm on the ground for Saturday morning, then clearing with 40-60 km/h northeast winds.

Avalanche Summary

An avalanche cycle was reported from the Terrace area during Monday and Tuesday's storm, although notably most of the avalanches appeared to be loose dry avalanches. Avalanches up to size 2.5 were also reported from the Ningunsaw area.

Snowpack Summary

Recent storms have deposited 50-80 cm new snow combined with strong, mainly southwest winds. Expect touchy wind slabs to have formed in the lee of exposed ridges. The storm snow has buried a layer of feathery surface hoar (up to 15 mm in sheltered areas), making wide propagations possible. A weak interface that formed during the early December cold snap can be found in isolated areas buried 100-150 cm deep. The layer consists of preserved surface hoar or weak faceted (sugary) snow. The lower snowpack is well consolidated in deep snowpack areas. In shallow snowpack areas, such as the northern part of the region, an old rain crust near the bottom of the snowpack has developed weak facets and might be triggerable from a thin or rocky area on a convex slope.

Problems

Storm Slabs

Storm slabs are 50-80 cm thick and growing with ongoing flurries and strong winds in the forecast. Storm slabs will be extra touchy in sheltered areas around treeline where they sit above preserved surface hoar.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.Use caution in lee areas. Recent snowfall mixed with wind loading has created storm slabs.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 3

Persistent Slabs

The additional load of storm snow may make it possible to trigger deeper weak layers that formed in isolated areas during the early December cold snap. These weak layers include facets and surface hoar that are buried 100-150 cm deep.

Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.If triggered the storm slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Dec 29th, 2016 2:00PM