Avalanche Forecast

Issued: Jan 5th, 2015 9:56AM

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

jlammers, Avalanche Canada

Kootenay Boundary.

The storm may be over, but we're not out of the woods. Forecast warming will have a continued destabilizing effect on the snowpack with the potential for very large avalanches. Conservative terrain selection remains critical.

Summary

Confidence

Fair - Freezing levels are uncertain

Weather Forecast

As the current storm pattern tapers-off, a warmer southwest air mass will over-ride the cooler remnant arctic air. The result will be light rain at ridge top elevations and freezing rain below treeline. A clearing pattern will evolve throughout Tuesday and will persist until Thursday as a warm, dry ridge of high pressure develops. Valley temperatures will remain below freezing for the forecast period; however, an inversion is forecast until Thursday with alpine temperatures exceeding zero degrees celcius each day. Ridgetop winds are forecast to peak at about 60km/h from the west on Tuesday morning, and then taper to about 20 km/h from the northwest for the rest of the period.

Avalanche Summary

At the time of publishing this bulletin, observations were extremely limited. In the wake of Sunday night's storm, I'm sure there was widespread storm slab activity with many avalanches stepping down to the mid-December crust/ surface hoar interface. With further loading on Monday (and subsequent warming), I'm sure we'll see ongoing large and destructive storm and persistent slab avalanche activity.

Snowpack Summary

Up to 40cm of new snow fell on Sunday night, with moderate southwest winds shifting these accumulations into deeper deposits in lee terrain. With more wind, snow and warming on the way, this potent new storm slab will likely remain sensitive to light triggers. The new snow overlies a variety of old surfaces which include heavily wind-affected surfaces in exposed locations, and faceted powder and buried surface hoar in sheltered terrain. Up to 100 cm below the surface, you'll likely find a touchy weak layer of surface hoar sitting on a thick rain crust. This widespread persistent weakness exists at all elevation bands, and continues to be the primary layer of concern for the region. With the current storm loading pattern, I expect this layer to increase in reactivity with the potential for large and destructive avalanches. At the base of the snowpack, a crust/facet combo appears to have gone dormant for the time being.

Problems

Storm Slabs

Continued storm loading will be followed by warming on Tuesday morning. This will add to the reactivity and destructive potential of this potent new storm slab.

Good day to make conservative terrain choices.>The new snow will require several days to settle and stabilize.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 4

Persistent Slabs

A weak layer which formed in December continues to produce avalanches under light loads, and is now buried by up to 100cm of snow. With the added stress of the new snow, avalanches at this interface are more likely, and could be highly destructive.

Good day to make conservative terrain choices.>Avoid steeper open slopes and convex rolls at all elevations.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

2 - 5

Valid until: Jan 6th, 2015 2:00PM