Avalanche Forecast

Issued: Dec 13th, 2015 10:14AM

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

ghelgeson, Avalanche Canada

Cariboos.

The danger has come down, but large human triggered avalanches remain possible. Start with small test slopes and build up slowly to the bigger terrain features. There is still a lot of uncertainty associated with this early winter snowpack.

Summary

Confidence

Low - Due to the number of field observations

Weather Forecast

High pressure dominates the weather pattern for the next few days. The next major weather maker is not expected in the Cariboos until at least Friday. MONDAY: Trace of snow, freezing level at valley bottom, light W wind at lower and mid elevations, moderate NW wind at ridgetop. TUESDAY: Trace of snow, freezing level at valley bottom, light W wind at lower and mid elevations, moderate NW wind at ridgetop. WEDNESDAY: No snow expected, freezing level at valley bottom, light NW wind at lower and mid elevations, moderate NW wind at ridgetop.

Avalanche Summary

Large natural sluffs to size 1.5 were reported from all aspects between 1300m and 2400m Saturday. The last significant observation was from Thursday when a large natural avalanche (size 2.5) was observed on a NE facing feature at 2000m.

Snowpack Summary

A string of storms between December 2nd and December 13th produced 80 to 150cm of storm snow in the Cariboos which is settling out at all elevations. You may find a brittle thin crust about 15 to 50cm below the snow surface as high as 1800m that was formed by rain and warm temperatures on December 8th. Below all the new snow lies the early December persistent weak layer. This weak layer manifests as an old sun crust on due south facing features in the alpine, large grained surface hoar below 1800m and small facets in isolated pockets. The surface hoar has been the primary concern lately, especially below treeline between 1400m and 1800m. Test profiles have been producing moderate resistant planar results on the surface hoar which suggests that it's becoming less sensitive to human triggering. Recent winds out of the south and southwest have formed wind slabs on lee features that are mainly confined to the alpine, but you may find the odd fresh wind slab at treeline too. The mid and lower portions of the snowpack are thought to be well settled.

Problems

Storm Slabs

The storm slab problem should be settling out quickly, but I would still be wary of steep unsupported features, slopes immediately lee of ridge crest, convexities, wind loaded chutes and rock outcroppings.

Avoid freshly wind loaded features and use ridges or ribs to sneak around these problem areas.> Start with simple terrain and take a curious/experimental approach to the snowpack. You may be able to step out into challenging and even complex terrain after learning more about the snowpack.>While unlikely, it is possible for storm slabs in motion on south facing alpine features to step down to a deeply buried crust resulting in very large destructive avalanches.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Persistent Slabs

A layer of buried surface hoar can be found below treeline between 1400m and 1800m. Test profiles suggest this interface varies widely in reactivity and remains sensitive to human triggering.

Avoid open slopes, convex rolls, burns, cutblocks and terrain traps when traveling below treeline. This is where buried surface hoar is best preserved and most volatile.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Dec 14th, 2015 2:00PM