Avalanche Forecast

Issued: Dec 13th, 2013 8:32AM

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

ccampbell, Avalanche Canada

South Rockies.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

Saturday: Chinook conditions expected on the east side of the divide with strong winds and temperatures up to 5 degrees between 1200m and 2500m elevation. Elsewhere, cloudy with scattered flurries are expected to bring no more than 5cm of new snow. Freezing levels expected to remain at or near valley bottoms with treeline temperatures around -2. Ridge top winds are expected to be moderate southwesterlies. Sunday and Monday: Chinook conditions are expected to persist east of the divide, while elsewhere a mix of sun and cloud with isolated light flurrries possible. Freezing levels rising as high as 1800m with strong westerly alpine winds.

Avalanche Summary

Reports from yesterday include a few thin fresh natural wind slab avalanches up to Size 1.5, and 2 Size 1.5 explosive triggered wind slabs running on older faceted snow with generally wide propagation, but slow moving.

Snowpack Summary

Light incremental snowfall is starting 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

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

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.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Valid until: Dec 14th, 2013 2:00PM