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Archived

Avalanche Forecast

Dec 3rd, 2016–Dec 4th, 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
3: Considerable
The avalanche danger rating in the alpine will be considerable
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. Use a very conservative approach to terrain and watch your exposure from avalanche paths above you.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

The dominating stormy weather pattern has come to an end. Unsettled conditions persist Sunday while the Arctic front descends south and brings cold air and outflow winds for the forecast period. Sunday: Cloudy with snow amounts 4-10 cm. Ridgetop winds will be light from the northeast and freezing levels will be at valley bottom. Alpine temps near -8.Monday: Mix of sun and cloud. Ridgetop winds will be light from the northeast with moderate outflow winds through the inlets.Tuesday: Sunny with alpine temperatures near -15. Possible alpine inversion. Winds light from the northeast.

Avalanche Summary

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 Sunday.

Snowpack Summary

Storm snow totals reached 30-65 cm by Saturday, 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.

Avalanche Problems

Storm Slabs

Touchy storm slabs still exist especially on leeward slopes that see more loading from the winds.
If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Use caution in lee areas in the alpine and treeline. Storm snow has formed touchy slabs.The new snow will requires several days to settle and stabilize.

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 will likely become reactive under the load of the new snow.
Avoid open slopes and convex rolls where buried surface hoar may be preserved.Minimize overhead exposure during periods of heavy loading from new snow, wind.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 2 - 3