Avalanche Forecast

Issued: Jan 13th, 2017 4:29PM

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.

mgrist, Avalanche Canada

Northwest Coastal.

Heavy snowfall and strong winds are a recipe for large destructive avalanches.

Summary

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain on Saturday

Weather Forecast

Strong winds plus an incoming storm with warmer temperatures are in stock. This will be an extended stormy period for the Northwest, with lots more to come on Monday. SATURDAY: An additional 10-20 cm of new snow, with higher amounts in the north of the region. Winds strong (60 Km/hr) from the southwest. Freezing level rising to 1000 metres with Alpine temperatures around -2 Celcius. SUNDAY: A brief lull in the action - some flurries and up to 5cm snow. Freezing levels around 1100m. Winds moderate to strong southwesterly. Alpine temperatures near -2 Celcius. MONDAY: The big wallop comes in the afternoon with 30-50 cm of new snow by the end of the day. Winds strong (60 Km/hr +) from the southwest. Freezing level rising to 1500m and alpine temperatures around -1 Celcius.

Avalanche Summary

On Thursday several Size 2 natural slab avalanches were seen just north of Terrace on east and west aspects near treeline, running mostly likely on the Jan 5/6 surface hoar. On Wednesday natural avalanches were observed on northern aspects around 1300m, running on the Jan 5/6 surface hoar layer.

Snowpack Summary

We've had 15cm new snow on Thursday into Friday near Stewart (and only 3-4 cm near Terrace). Expect this new snow (and all the snow that will come on Saturday) to bond poorly to all the windslabs that formed during the latest arctic outbreak winds. Those strong arctic winds (southeast through northeast) redistributed the 20-40 cm of snow from a week ago at all elevation bands... and it sits on a variable interface composed of hard wind slabs, weak surface hoar (Jan 5/6 layer) and faceted snow. The net result is touchy slabs on wind-loaded features that are giving easy to moderate sudden results in snowpack tests. Below the new snow, a well settled slab sits above the Christmas surface hoar layer which is well preserved in southern areas. This surface hoar is now buried 60-100 cm deep, and is still reactive in sheltered areas and steep open features at and below treeline. Deeper weak layers have only been reactive in areas with thin snowpacks. This includes a facet layer from early December that has been reactive in snowpack tests at lower elevations in the southern part of the region, and weak facets near the ground that have produced avalanches in the northern part of the region.

Problems

Storm Slabs

All the incoming snow is not expected to bond well at all to the windslabs created during the past week.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Minimize exposure during periods of heavy loading from new snow and wind.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

Weak layers of surface hoar are now buried up to 1.2 metres deep and may be more reactive after the recent loading. Take extra care to avoid thin trigger points and exposure to overhead hazard.

Be aware of the potential for large avalanches due to the presence of buried surface hoar.Use conservative route selection, stick to moderate angled terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Jan 14th, 2017 2:00PM