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Avalanche Forecast

Archived

Dec 9th, 2012–Dec 10th, 2012

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

Regions

Kootenay Boundary.

Confidence

Fair - Intensity of incoming weather is uncertain on Tuesday

Weather Forecast

Overnight and Monday: Light precipitation and moderate Westerly winds overnight are expected to shift to the NW during the day and become gusty up to 60 km/hr. Freezing level should be about valley bottom, and alpine temperature about -7.0Tuesday: Expect the winds to shift to the West as the trailing cold front moves through the region bringing 5-10 mm of precipitation and freezing levels at about 1000 metres. The alpine temperature should be about -6.0.Wednesday: There should be a bit of a dry spell during the day with light NE winds. Alpine temperatures near -10.0

Avalanche Summary

Some natural avalanches that were at least 24 hours old were reported from near Kootenay Pass that were size 2.0 and about 25 cms deep. Near Nelson, explosives control produced size 1.0 soft slab avalanches up to 20 cms deep.

Snowpack Summary

The Kootenays have received over a metre of snow over the past week, with Kootenay Pass seeing the highest amount regionally. Regardless, current surfaces most likely include varying amounts of fairly low density storm snow which override wind slabs that formed earlier in the week. Below the recent storm snow exists a surface hoar layer that was buried at the end of November. Recent tests on this layer show CTM (SP) down 100 cm sliding on surface hoar 4-10 mm in size. Near the base of the snowpack sits the early November rain crust. This layer is most likely to be found in deeper snowpack areas at higher elevations. I'm not aware of any activity on this layer in the KB region; however, deep and destructive releases have been observed in the South Columbia region (directly to the north). Keep this on your radar, especially when traveling in areas at higher elevations that have a smooth ground cover where the existing crust is uniform and consistent. Average snowpack depths at treeline are 130-200 cm. There are significant variations in snowpack structure from one drainage to another. In short, digging down and making your own observations will be critical to safe slope selection.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.