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Archived

Avalanche Forecast

Dec 4th, 2016–Dec 5th, 2016
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
Below Threshold
The avalanche danger rating below treeline will be below threshold
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
Below Threshold
The avalanche danger rating below treeline will be below threshold
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
Below Threshold
The avalanche danger rating below treeline will be below threshold

Regions: Northwest Coastal.

Rider triggered storm slab avalanches are likely, especially where there is buried surface hoar. Use a very conservative approach to terrain and gather info while you travel.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

A cool arctic air mass will dominate the weather pattern over the next few days bringing cooler and much dryer conditions. Coastal areas may see some flurries and cloudy skies tonight and early tomorrow before the arctic front locks in on Tuesday. Skies will mostly be a mix of sun and cloud. Alpine temperatures will drop to -15 accompanied by light NE winds. Expect strong, cold outflow winds.

Avalanche Summary

On Saturday, ski tourers reported numerous persistent slab avalanches triggered remotely and running on the buried surface hoar interface. The avalanche crowns  were 50-100 cm deep, 200 m wide and 100 m long from northeast aspects at upper elevations. They also noted another avalanche from a distance away running 500 m in length and width. Rider triggers are likely on Monday where this instability exists.On Friday, explosive triggered storm slabs were reported from northerly aspects at 1400 m and above up to size 2.5. Some of these ran on the buried surface hoar layer. At treeline and lower elevations numerous loose wet natural avalanches were reported from steep, rocky terrain features. Natural avalanches are still possible and rider triggered avalanches remain likely through Monday. Light winds from the northeast may reverse load slopes and catch you by surprise.

Snowpack Summary

Storm snow totals reached 30-75 cm by Sunday, with the potential for much more on lee features due to strong southwest winds. The new snow buried a surface hoar layer reported 60-100 cm below the surface in many parts of the region. This layer was reportedly reactive during the storm. 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.

Avalanche Problems

Storm Slabs

Touchy storm slabs still exist especially on leeward slopes that see more loading from the winds.
The new snow will requires several days to settle and stabilize.Caution in lee areas. Switching winds may reverse load slopes and catch you by surprise.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 2

Persistent Slabs

Persistent weak layers with surface hoar, facets, and crust are buried 60-100 cm deep throughout the region, and reportedly became reactive during the storm.
Avoid slopes where buried surface hoar is preserved. Remote triggering from a distance is possible.Dig down to find and test weak layers before committing to a line.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 2 - 3