Avalanche Forecast

Issued: Dec 21st, 2011 9:31AM

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

mpeter, Avalanche Canada

South Columbia.

Check out the forecaster's blog for more info on the variability within the region.

Summary

Confidence

Good - -1

Weather Forecast

Thursday: Expect dry conditions with mostly clear skies. Winds should shift from northerly to westerly and reach 40-60 km/h at ridgecrests. Freezing levels may reach 1300m. Friday: Dry conditions persist with continued westerly winds and freezing levels reaching 1500m. Saturday: A chance of flurries on the west side of the region, dry elsewhere. Winds turn southwest and increase to strong values at ridgecrest with freezing levels climbing as high as 1800m.

Avalanche Summary

Avalanche activity has slowed down, but both human and naturally triggered avalanches are still being reported up to size 2.5. These have been on all aspects and elevations, with notable involvements in gladed terrain below treeline. The avalanches are failing on the surface hoar buried between December 11-14 and are much more prevalent in the northern end of the region.

Snowpack Summary

A north-south split exists in this region at present as a result of the track of recent storms. Northern and western areas have seen up to 50 cm of recent storm snow, while areas further south have seen more like 20cm. This storm slab is reported to be upside-down, which means higher density snow sits on top of less dense snow. The storm slab sits above a well developed surface hoar layer from mid December, which has been reacting readily to snowpack tests and ski cutting. Additionally, remote-triggered avalanches have been reported on this layer, indicating it has a high potential for fracture propagation. All this info points to the same thing: Where the storm slab is sufficiently thick (in the order of 40 cm) and cohesive, conditions are ripe for slab avalanches. Lower in the snowpack, the mid-layers are well-consolidated and strong. Near the base of the snowpack there are a few layers that have the potential to wake up with a really big storm or very heavy loads (such as a sled airing off a cornice). These include a surface hoar layer from early November, a crust/facet combo from October and the interface on steep glaciated terrain with snow that did not melt over the summer.

Problems

Persistent Slabs

Slab avalanches are now occurring on the mid-Dec surface hoar interface in northern parts of this region (think a band between the TransCanada and a line 50 km to the south). All aspects. Elevation from 1400m to 2300m. Remote triggering possible.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 5

Wind Slabs

Wind slabs are sliding easily on the recently buried surface hoar. Shifting winds have set up this problem on a variety of aspects, particularly north through south east.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Valid until: Dec 22nd, 2011 8:00AM