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Avalanche Forecast

Archived

Dec 10th, 2012–Dec 11th, 2012

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Kootenay Boundary.

Confidence

Fair - Intensity of incoming weather is uncertain on Tuesday

Weather Forecast

Overnight and Tuesday: A warm front is moving across the region tonight and a trailing cold front should move through the region in the morning. The North of the region should get 5-10 mm starting in the early morning. The South may be quite a bit drier (4-6 mm). Strong NW winds overnight should become moderate to strong Westerly during the storm. Alpine temperatures should be -9.0 and the freezing level may rise to 700 metres during the storm.Wednesday: There is a weak ridge between systems that should bring very light precipitation, light Northerly winds and temperatures down to -10.0 in the alpine.Thursday: The next frontal system is looking weak at this time. Expect light precipitation and SW winds. Check back tomorrow for an update.

Avalanche Summary

Some very soft slab avalanches up to size 1.5 were reported near Nelson from explosives control.

Snowpack Summary

There has been a lot of unconsolidated surface snow that has been producing heavy sluffing in steeper terrain. It sounds like the wind is starting to transport some of this light surface snow into wind slabs. If the wind has not affected the snow yet, it probably will by morning. There is still concern in this region for the late November surface hoar that is buried about 100-125 cms. New wind slabs and the recent storm snow may be enough of a load to make this weakness reactive to light additional loads. There was some discussion about a thin variable crust that formed around the 5th of December. We have not heard any concern about this lately, do you see it in your local area?

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.