Avalanche Forecast

Issued: Dec 2nd, 2016 4:41PM

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

swerner, Avalanche Canada

Northwest Coastal.

The storm continues bringing more snow and strong winds overnight. Add this to a buried weak layer and you have the perfect recipe for dangerous avalanche conditions.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

Snow and strong to extreme winds from the West will persist overnight and into Saturday with coastal regions seeing the brunt of the storm. The centre of the low will weaken over the Gulf of Alaska while most of the BC coastal regions stay unsettled. An arctic front will push its way towards the BC North Coast on Sunday afternoon and strong outflow winds are expected through coastal inlets during this period.Saturday: Freezing levels near 500 m with alpine temps near -4.0. Snow amounts 10-25 cm and ridgetop winds strong from the West.Sunday: Freezing levels near 300 m with alpine temps near -8.0. Snow amounts 8-15 cm and ridgetop winds light with strong gusts from the southwest. Monday: Mix of sun and cloud with freezing levels in the valley bottom and alpine temps near -9.0. Ridgetop winds light from the East. Expect outflow winds.

Avalanche Summary

On Thursday, several machine triggered storm slab avalanches were triggered up to size 3 from North aspects between 1400 m- 1500 m. These were 25-100 m wide and running 20-180 m in length, running on buried surface hoar. Explosive control also triggered several size 2 slabs on East aspects within that same elevation zone. No new avalanche reports from today (Friday) however; a widespread natural avalanche cycle likely occurred during the storm and will persist with strong winds and more snow.

Snowpack Summary

Storm snow totals reached 30-50 cm by Friday afternoon, with the potential for much more on lee features due to strong winds. The new snow will load a buried surface hoar layer reported 60-80 cm below the surface in many parts of the region. Recent snowpack tests indicated the layer can be triggered with moderate loads and has the potential to propagate over long distances. This layer will likely become reactive under the stress of this new load. A thick rain crust exists 20-30 cm below the surface hoar layer, with isolated reports of weak facets (sugary snow) forming above the crust. Treeline snow depths are around 120-140 cm in the Terrace and Stewart areas, but substantially less further north. Snow in these thinner areas, such as Ningunsaw, may be faceting and developing weak basal layers.

Problems

Storm Slabs

Touchy storm slabs continue to build with new snow and strong winds.

If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Very Likely - Certain

Expected Size

1 - 3

Persistent Slabs

Persistent weak layers with surface hoar, facets, and crust are buried 60-100 cm deep throughout the region, and will likely become reactive under the load of the new snow.

Minimize overhead exposure during periods of heavy loading from new snow, wind.Avoid open slopes and convex rolls where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

2 - 3

Valid until: Dec 3rd, 2016 2:00PM