Avalanche Forecast

Issued: Dec 5th, 2014 8:53AM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Storm Slabs and Persistent Slabs.

ghelgeson, Avalanche Canada

Kootenay Boundary.

Riding north of Nelson? Take a look at the South Columbia forecast too. Please email your observations to forecaster@avalanche.ca

Summary

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

5- 15 cm of fresh storm snow is coming to rest on either crust, surface hoar or snow that has become weak with the recent cold temps. Add in SW winds, and it's likely that shallow yet sensitive wind slabs will form in exposed terrain.

The weekend avalanche problem should be pretty manageable: avoid terrain traps and practice good travel techniques. Watch for wind slabs as you gain elevation and ski penetration decreases.>Choose terrain that offers multiple options, good escape routes and have a plan to manage wind slab avalanches.>Conditions are changing, so stay flexible with your travel plans. Be prepared to retreat to simple terrain if need be.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

There are a few deeply buried weak layers in the snowpack. Not a lot is known about this structure, but it's likely that trigger-ability will increase as it's snowing and blowing.

Avoid spots where you're more likely to trigger large avalanches: thin spots, rock out-croppings, convex rollers and broad planar slopes without anchors like trees.>Every avalanche has the potential to step down to the ground right now, you need to manage your behavior and terrain use to account for that possibility.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 5

Valid until: Dec 6th, 2014 2:00PM