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Avalanche Forecast

Archived

Dec 5th, 2014–Dec 6th, 2014

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

Regions

Kootenay Boundary.

Riding north of Nelson? Take a look at the South Columbia forecast too. Please email your observations to [email protected]

Confidence

Poor - Due to the number of field observations

Weather Forecast

Synopsis: A pattern shift is underway as dry and cold northwest flow gives way to rather mild southwest flow. Storm totals through the weekend look rather modest, but the door appears to be open to a succession of storms through the middle of next week.Friday: Precipitation: 1-3mm | 2-5cm; Wind: Moderate, SWSaturday: Freezing Level: 600m; Precipitation: 3-12mm | 4-15cm; Wind: Treeline: Light, SW | Ridgetop: Moderate/Strong, SW Sunday: Freezing Level: 800m; Precipitation: Trace: Treeline: Light, SW | Ridgetop: Moderate, SWMonday: Freezing Level: 1000m; Precipitation: 0-3mm | 0-5cm; Wind: Treeline: Light, SW | Ridgetop: Moderate, SW

Avalanche Summary

We received an observation of a small natural avalanche from the Kokanee Glacier Park on an east facing slope just below treeline. This avalanche failed on the early November crust/facet combo near the ground. Subsequent testing produced inconsistent sudden planar results. While it's technically just north of this region, I suspect that this is a pretty good example of the snowpack structure in the region north of Nelson.

Snowpack Summary

This forecast is based off a very limited data set. The snowpack north of Nelson is a different beast, if you're riding in that part of the region, check out the South Columbia forecast to get a feel for the more complex snowpack and the associated persistent slab problem.Across the region the Black Friday storm came in wet and finished cold. This left a supportive (pencil/knife) crust 2 - 8cm thick which is present to around 2000m. 15 - 30 cm of snow from the tail end of that storm now rests on this crust. Winds have been pretty mild since the storm, but I suspect you can find the odd wind slab in exposed terrain.In the north it appears there are three layers of concern: The late November crust at or just below the surface; the mid November surface hoar/facet/crust combo down 70 - 90 cm; and the early November hard crust/facet combo near the ground. In the southern portion of the region observations indicate that the snowpack is more homogeneous and strong, but the early November hard crust/facet combo is present in some locations. Just how widespread this is, I don't know. We'd be stoked to see your observations this weekend! 

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.