Avalanche Forecast

Archived

Dec 11th, 2014–Dec 12th, 2014

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 unlikely, human triggered possible.

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

South Columbia.

Although the trend shows improvement remember that the potential for triggering an avalanche is greatest at higher elevations due to recent heavy snowfall and strong winds.

Confidence

Fair

Weather Forecast

One last system is expected to cross the province tonight bringing moderate precipitation and strong winds while maintaining high freezing levels. We could see 10-15 cm by midday Friday. Freezing levels on Friday should start near 2000 m but should drop to 1500 m late in the day. Winds are strong from the Southwest easing to light from the Northwest. The weekend looks much drier with a mix of sun and cloud. Freezing levels around 1000 m on Saturday and 500-700 m on Sunday. Winds remain light.

Avalanche Summary

Widespread natural avalanche activity up to size 3 was reported on Tuesday and Wednesday. These were primarily storm slabs in wind loaded areas. The bed surface may have been the Dec 5 surface hoar layer and/or the late-November rain crust. Slab depths are typically 30-60 cm but one report has a slab depth up to 150cm, likely in a heavily wind loaded area. Loose wet slides were also reported in lower elevation terrain.

Snowpack Summary

There are recent reports of wet snow up to 2000m elevation and moist snow to around 2400m. Higher elevations could have received 30-50 cm of dense storm snow. Strong winds are loading leeward features in the alpine. Below the new storm snow may be a layer of surface hoar which was buried on Dec 5. Below around 1800m elevation and down around 40-50cm is a rain crust but it appears that the snow above it is generally well bonded. About 1m down, a weak layer of surface hoar and/or facets can be found in some locations. A thick rain crust with facets from early November is buried over 1 m down. Snowpack tests on these deep weak layers are showing slowly improving results, but in some locations these layers are still reactive and have the potential to release large slab avalanches. We may see these deep weak layers become a problem again as the storm continues to add new load.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.