CANADIAN AVALANCHE ASSOCIATION BACKCOUNTRY BULLETIN _12 DECEMBER, 1996_ _SOUTH COAST & VANCOUVER ISLAND_ _WEATHER:_ Daily accumulations of 10-20cm of new snow have continued, and light to moderate winds have transported this into lee areas. Yet another low pressure system is developing in the Pacific, and is expected to begin affecting the southern portions of the coast by late Friday. Moderate winds, and additional new snow can be expected for the weekend. _SNOWPACK:_ The instabilities within the storm snow have begun to tighten up, but the depth of snow overlying a weak facet layer has exceeded 1 metre in some areas. This deep instability is presently reacting to explosives and could potentially be responsible for more widespread natural or skier triggered activity with additional loading. In northern areas of the coast, the snowpack continues to be shallow . _AVALANCHES:_ Some natural activity in the storm snow continues, although this is lessening. Very large avalanches (some with fracture lines in the 2.5 to 4 metre range), are being reported with explosive use, and indicate the potential for size 2.5 to 3.5 skier triggered avalanches exists, especially in lee areas at treeline and above. _DANGER:_ Although natural activity is lessening, the danger is _CONSIDERABLE_ in south and central areas of the Coast, due to the size and destructive power of the avalanches failing on the deep facet layer. The danger in the Duffy Lake area is_ MODERATE_, with reports of pockets of deep instability remaining. _TRAVEL ADVISORY:_ Pay close attention to the weather over the weekend, and evaluate each suspect slope from the point of view of , "What would happen if this whole slope released to 1 metre depth." _NORTH COLUMBIA_ _WEATHER:_ Up to 1 metre of new snow has blanketed the area in the past 10 days. A weak upper trough may produce light new snow in some areas on Friday, and a low approaching the south coast increases the chance of snow for the weekend. _SNOWPACK:_ Snowpack depths are generally in the 2 metre range now, about average. The storm snow continues to produce natural avalanches throughout most of the region, and a weak facet layer buried from 100 to 130cm deep has reached threshold. This deep instability overlies a rain crust in many areas, making an excellent bedding surface for avalanches to propagate to quite large size. _AVALANCHES:_ Throughout the region, natural avalanches to size 2 continue to run in the storm snow. There are reports of skier triggered avalanches propagating to size 2.5, particularly at and above treeline. Many areas are reporting whumphing and settlements around skiers and snowmobilers, so additional new snow is a concern. _DANGER:_ _CONSIDERABLE_ at treeline and in the alpine. _TRAVEL ADVISORY:_ Any new snow which occurs over the weekend should be cause for concern. Even if very little avalanche activity is observed, do not rule out the possibility of human triggered avalanches of large size, and choose your terrain accordingly. _SOUTH COLUMBIA_ _WEATHER:_ Recently, the weather pattern in the region has promoted the tightening up of the snowpack. Some new snow may occur over the weekend, and moderate South to South West winds should prevail. _SNOWPACK:_ The region has received up to 80cm storm snow over the last week. Widespread natural activity occurred in the upper snow layers on Monday, and this has generally begun to taper off as the storm snow settles. The deep facet layer causing concern in other portions of the province is less developed in the south. Some areas are reporting surface hoar with small amounts of new snow overlying, which may form a problem layer in the future. _AVALANCHES:_ Widespread reports of size 1 to 2 avalanches occurring in the storm snow on Monday, tapering off as the week progressed. Wind transported snow is responsible for the majority of the natural activity. _DANGER:_ MODERATE, although pockets of instability remain. _TRAVEL ADVISORY:_ Wind transport of snow should be on your mind this weekend. Steep rolls and seemingly insignificant terrain features on lee slopes can still be a concern. _ROCKIES_ _WEATHER:_ The Rockies have once again taken the prize for variability across the region, both in weather and snowpack. From the Sunshine area south to the US border storm snow accumulations of 20cm in the last day or two have occurred, while the north half of the region has remained dry. Little new snow is expected over the weekend, with the only strong possibility existing in the extreme south. Waterton daytime temps are above zero. _SNOWPACK:_ Total snowpack ranges from half a metre in the Jasper area, to 2 metres in the extreme south. The north snowpack has faceted, and will be an area of concern later in the season once more new snow arrives. Wind transport in the Banff and Kananaskis areas is overloading start zones on lee slopes. The south has stabilised, although most areas report the deep facet layer giving problems in other parts of the province is evident in areas where naturals have not run. Waterton has isothermal surface conditions from above zero daytime temps. _AVALANCHES:_ Very little natural activity is reported in the north. Wind transport has caused widespread natural activity in the Banff/Kananaskis area, with a size 3 avalanche propagated by a skier dropping into Purple Bowl in the Lake Louise area reported. Very little natural activity is occurring in the south, although wet surface avalanches are running later in the day in Waterton. _DANGER:_ _CONSIDERABLE_ in northern and central areas of the Rockies, _MODERATE_ in the south. The main danger exists from triggering an avalanche in shallow snow which could propagate into deeper snow nearby. Watch the facet layer deep in the pack in southern areas. _TRAVEL ADVISORY:_ Spread your party out, watch out as you drop into bowls from areas with shallow, weak facets. Take your pits down deep in the south to have a look at the weaker facet layer in the lower half of the pack. The Bulletins will be issued on Monday and Thursday. THIS BULLETIN ALSO SPONSORED BY MOUNTAIN EQUIPMENT COOP _________________________________________________________________ Contact numbers for the Avalanche Bulletin are: