Avalanche Forecast

Issued: Dec 14th, 2013 8:08AM

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

rbuhler, Avalanche Canada

South Rockies.

Summary

Confidence

Fair

Weather Forecast

Weather conditions are expected to vary substantially across the forecast region with Chinook conditions influencing the eastern part of the region and a westerly zonal flow influencing the western region. Generally dry conditions are expected across the region until Tuesday or Wednesday.Sunday: A mix of sun and cloud, freezing levels are expect to rise, possibly as high as 1800m (higher in the eastern regions), temperature inversion conditions likely, and strong alpine winds from the west for most of the region, Monday: Mostly sunny conditions, freezing levels around 2000m (higher in the eastern regions), moderate alpine winds from the west for most of the regionOutlook: A lot of uncertainty/conflicts in the weather models for Tuesday and onwards. The Pacific westerly zonal flow is expected to replace the warm Chinook air but the timing is uncertain and it could occur on Tuesday or Wednesday. This will result in colder temperatures and light precipitation.

Avalanche Summary

No natural avalanche activity reported since Thursday. On Friday, explosive control resulted wind slab avalanches up to size 1.5 in both the Fernie and West Castle areas.

Snowpack Summary

Light incremental snowfall has started to bury surface hoar and a faceted upper snowpack. Snowpack depths at treeline seem to vary from 50 - 110 cm with high variability in wind-exposed areas. Buried surface hoar and facets, with an associated crust, are down approximately 30-40cm. Recent snowpack testing on this persistent weakness gave easy results and some whumpfing. The base of the snowpack is made up of weak facets and depth hoar. This deep persistent weakness may be stubborn to trigger, especially in deeper snowpack areas, but the sensitivity to triggers likely increases in shallower locations, especially on a steep, convex slopes. In some areas it is below threshold below treeline, and early season hazards like open creeks, and stumps exist.

Problems

Wind Slabs

Wind slabs have developed recently on a variety of aspects due to shifting winds. Expect to encounter these deep deposits of wind-transported snow below ridge crests and behind terrain features.

Be cautious as you transition into wind affected terrain.>Be careful with wind loaded pockets. Be aware of wide variation in snowpack depth>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Persistent Slabs

Sugary facets at or near the base of the snowpack are most likely triggered on steep, convex slopes with a thin snowpack. In deeper snowpack areas you may find a stubborn buried surface hoar layer.

Whumpfing, shooting cracks and recent avalanches are all strong inicators of unstable snowpack.>Dig down to find and test weak layers before committing to a line.>Avoid shallow snowpack areas on steep, convex terrain where triggering is more likely.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Valid until: Dec 15th, 2013 2:00PM