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Backcountry Advisory

January 16, 2008

Alpine: Moderate

Treeline: Moderate

Below Treeline: Low

Travel Advisory: Monday’s storm cycle brought a total of 25cm of new snowfall, accompanied by southeast winds gusting to 100 km/h at alpine elevations. Temperatures reached zero degrees Celsius at 1,835 metres with the arrival of the storm, rapidly falling with its passage. There has been significant drifting at alpine and treeline elevations and the resulting slabs are quite stiff. You can expect that the alpine terrain has developed many new features. Be wary of any hard, hollow feeling areas of windslab, and keep in mind that large unpredictable avalanches are still very much a possibility. Reverse loading from northwesterly winds this week could form some new surface instabilities on more southerly aspects.

Avalanche Activity: Explosive testing yesterday produced results predominantly up to size 1.5 within the storm snow layers, with crowns averaging 10-20 cm in depth. Cornices have grown and were failing easily. Deep slab releases are continuing to occur sporadically with both large and small explosive triggers. One anomalous result was a size 3.5 with a fracture line up to 3.5 metres in depth produced with a 25 kg charge. It ran on the Dec. 4 crust and facet layer.

This occurrence corresponds with similar deep slab releases on Blackcomb yesterday, and periodically during the past week in various backcountry regions. There has been evidence of a fairly widespread natural avalanche cycle having occurred during the storm, predominantly within the storm snow layers. You can expect to see lots of new cornice buildup – a falling cornice chunk could be the trigger to get a large avalanche moving.

Snowpack: The snowpack over the alpine terrain is quite variable due to the strong winds accompanying the storm. You can expect to encounter wind scoured areas, as well as areas of sustrugi and very stiff windslab. Temperatures fell dramatically after the passage of the storm which helped the storm snow layers to tighten in. The Dec. 4 raincrust and facet crystal weakness continues to get buried deeper, but the crust can still be found on the surface in some wind-affected terrain. Although this buried weakness has gradually been gaining strength, it continues to pop up sporadically, with the resulting avalanches getting larger and larger as the overlying snowpack grows. Its unpredictable nature is problematic and backcountry travelers should be cautious. The deep slab releases appear to be failing in a shallow part of the slab, propagating into the fatter part of the slope. Rocky unsupported start zones seem to be a common quality in these deep slab releases. This persistent weakness is expected to be with us for some time to come.  

Weather: A series of weak systems to the North will brush by our region periodically over the next several days bringing a mix of sun, cloud, and a chance of scattered flurries. Temperatures will remain cool. A more organized system may arrive on Friday or Saturday.

Travel with a partner and be equipped and prepared for self-rescue. Watch out for winch-cats or snowmobile traffic if you re-enter the area after operating hours.

Whistler Mtn. Snow Safety