Avalanche Forecast

Issued: Jan 2nd, 2015 7:53AM

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

jfloyer, Avalanche Canada

Purcells.

A crust/surface hoar layer from mid-December remains the primary concern and requires careful terrain selection. New snow may conceal wind slabs in exposed terrain.

Summary

Confidence

Fair - Intensity of incoming weather systems is uncertain on Monday

Weather Forecast

Saturday: mostly cloudy with flurries. Treeline temperatures around -13C and winds light or moderate from the west. Sunday: Dry during the day with snow starting late in the afternoon. Treeline temperatures around -16C, winds light and variable. Monday: 10-20 cm new snow expected by the end of the day Monday. Freezing levels are expected to remain below valley bottom, with treeline temperatures around -10C. Winds anticipated to rise to around 50 km/h from the southwest.

Avalanche Summary

Explosives control on Thursday produced several avalanches generally in the 1.5 to 2.5 size range with some of these failing on persistent weak layers, while others only involved surface snow. One very large avalanche (size 3.5) was explosively triggered that released on an early season weak layer with a deep, 3 m crown and very wide propagation. A small (size 1) skier-triggered avalanche was reported from near Golden on a steep convex roll in forested terrain at 2200 m on a northeast aspect.

Snowpack Summary

Most of this region only saw light snow accumulations during the storm that ended Friday. However, winds were sufficiently strong for fresh wind slabs to be of concern. Since previous winds were from the north and more recent winds anywhere from southwest to northwest, wind slabs should be suspected on a wide variety of aspects in exposed terrain. A spotty thin layer of surface hoar was buried on December 27th by about 5-10 cm of light dry snow. As more snow accumulates, this interface could become one to watch. Deeper, at about 40-60 cm below the surface, a persistent crust/surface hoar layer from mid-December can be found. Recent snowpack tests show moderate "pops"-type results on this layer, indicating the potential for avalanches to propagate if triggered on this layer. This persistent slab problem is reasonably widespread across the region and is not expected to improve quickly. A deeper crust/facet layer which formed early in the season may still be triggerable from thin or rocky snowpack areas.

Problems

Persistent Slabs

A buried crust/surface hoar layer demands respect. It has been easy to trigger with light loads (like a person). This layer is down about 30-50 cm in most areas, but may be deeper where wind slabs have developed.

Stick to small features with limited consequence and be aware of what is above you at all times.>Choose well supported terrain without convexities.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 5

Wind Slabs

Recent strong winds have left wind slabs behind on a variety of slopes. Particularly on southern aspects, they may have become hidden under a dusting of new snow.

Use ridges or ribs to avoid pockets of wind loaded snow.>The recent snow may now be hiding windslabs that were easily visible before the snow fell.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Jan 3rd, 2015 2:00PM