Avalanche Forecast

Issued: Jan 12th, 2017 4:17PM

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

mgrist, Avalanche Canada

Northwest Coastal.

A complex pattern of wind slabs has developed at higher elevations. Below it, a persistent slab is waiting for the right trigger.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Saturday

Weather Forecast

Significant change is on the way, and it will be warming up as well. We're at the start of a stormy period for the Northwest, and the snow could really ramp up Sunday night. FRIDAY: Flurries bringing approximately 10-20 cm of new snow to the south and 20-30cms to the Stewart area (more in the western portions). Winds strong (60 Km/hr +) from the southwest. Alpine temperatures around -5 Celcius and rising overnight. 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 1200 metres with Alpine temperatures around -2 Celcius. SUNDAY: A brief lull in the action - some flurries and up to 5cm snow. Freezing levels temporarily dropping to 1000m. Winds moderate to strong southwesterly. Alpine temperatures near -3 Celcius.

Avalanche Summary

With the temperature inversion yesterday (warming almost to 0 degrees at 1400m) there were natural avalanches observed on northern aspects around 1300m, running on the Jan 5/6 surface hoar layer.

Snowpack Summary

Recent strong winds (southeast through northeast) have redistributed the 20-40 cm of snow from Friday-Saturday at all elevation bands. This snow 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

Wind Slabs

Strong northeast through southeast winds have built touchy slabs above a variety of weak layers. Skillful routefinding will be required to navigate around these slabs at treeline and above.

Be alert to conditions that change with aspect and elevation.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be cautious as you transition into wind affected terrain.

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

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.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Jan 13th, 2017 2:00PM