February 1, 2001 NOTICE OF UNUSUAL AVALANCHE CONDITIONS: Valid until further notice. This season avalanche professionals between the Inner Coast Mountains and the Rocky Mountains have observed snowpacks that are unusually weak. The combination of below normal snow depth and low temperatures has produced layers of facetted grains and surface hoar with a low strength. These types of weak layers can persist for a long time, and the avalanche danger will increase with every load of new snow onto this weak base. The present snowpack is less stable than in most other years and remarkably different from the snowpack at the same time last winter. Back country users will have to pay much attention to snowpack structure and strength during this winter. Note: Check out the new updated Western Canadian Avalanche Information on the CAA website, at www.avalanche.ca\Bulletin.html. The new page provides quick and easy access to every bulletin available on the web in Western Canada. One stop shopping, including bulletins, weather, satellite imagery, road conditions, and coming soon, interactive discussion boards on regional conditions! SOUTH COAST REGION WEATHER: Although temperatures remained reasonable, snow continued to fall intermittently, with a good dose of wind mixed in. The weather forecast calls for the winds to continue until Friday, with at least 10cm more snow as well. By Saturday, a ridge of high pressure will build, clearing skies, calming winds, and cooling the temperatures down a bit, particularly the overnight lows. SNOWPACK: Wind slab continues to be a problem in the alpine and at treeline, and this will get worse if the weather forecast holds true. A surface hoar layer from treeline down is buried under the storm snow, and fails with ski cutting, particularly in openings where it was most developed before burial under the storm snow. The warm temperatures are promoting settlement, and when things cool off, the surface should tighten up with overnight cooling, forming a crust at low elevations. The deep November facets will be most threatening in shallow snowpack areas. Treeline will represent the greatest hazard, from wind slab over surface hoar. AVALANCHES: Surface slabs would react to ski cutting in the alpine, but would run naturally only on steep slopes. Below treeline, the storm snow was prone to release on buried surface hoar, but that may improve with weekend cooling. No full depth releases were seen yet for this storm period. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (Feb 5th) ALPINE ^Ö Considerable, improving later TREELINE - Considerable, improving later BELOW TREELINE - Moderate TRAVEL ADVISORY: Shallow transition zones, where forces penetrate into the November facet layer more readily, will be the tricky snowpack situation to be on guard for. Watch the wind slab for a while yet, particularly at treeline. Hopefully, skies are clear by Saturday, providing good glacier touring. NORTH COLUMBIA REGION WEATHER: Snow worshipers dance in the streets in Revelstoke! Storm snow of 40-50cm now lies in the alpine, although it got a good pounding from wind earlier in the week. The forecast calls for another weather system to track through Friday, bringing one last shot of snow before a ridge of high pressure builds Saturday, clearing skies and bringing cool overnight lows to the alpine. SNOWPACK: The storm snow is wind affected in the alpine, with a stiff slab in some exposed areas. Beginning at treeline, the snow buries a surface hoar layer which should be down about 40cm from the surface at treeline by the weekend. This is and will continue to be a failure plane, although the cooling trend may help here. The November facet layer is still not reacting, but the new load will be stressing the supporting slab which lies above the facets, particularly in shallow areas, where human triggering will be more likely. AVALANCHES: A widespread cycle of natural avalanches to size 3 spread through the north parts of the region, particularly in the Caribou range. Further south in areas like Roger^Òs Pass, less activity was observed. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (Feb 5th) ALPINE ^Ö High, areas of Considerable TREELINE ^Ö High BELOW TREELINE - Considerable TRAVEL ADVISORY: Watch terrain near treeline, where wind loading, buried surface hoar, and temperature transitions are all most pronounced. With more snow and wind in the forecast, and the fact that in some areas very little avalanche activity has occurred so far, it may be easy to begin to think this snowpack will react like it would in an average year. Resist building your confidence in this winter^Òs snowpack too far, after the sustained wind and snow loading we have seen this week, even if very few natural danger signs are present this weekend. SOUTH COLUMBIA REGION WEATHER: Weather across the South Columbias has been highly variable, with 10cm of storm snow occurring in the Purcells and up to 40 in the Selkirks and Kootenays. Winds remained light except for an 18 hour pulse of high winds out of the south west Tuesday. The forecast calls for another low to track directly over the region Friday, bringing more snow accompanied once again by strong winds. Saturday, temperatures will drop and skies will clear as a ridge of high pressure builds until early next week. SNOWPACK: Many exposed areas have a wind slab at the surface. On south aspects, the storm snow is often poorly bonded to a sun crust underneath. In sheltered areas, surface hoar lies buried under the storm snow. The snow that had arrived by Thursday and the snow predicted combine to make it likely the deep faceted layer near the ground, formed in November and somewhat unreactive as of yet, may spring to life this weekend. AVALANCHES: Storm snow avalanches are being reported throughout the region, even in areas which received very little snow. In the Purcells, slides are stepping down to the November facet layer and running full depth. With more snow and high winds in the forecast, things could get worse. By Saturday, natural activity may taper off, but the potential for human triggering will linger throughout the weekend. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (Feb 5th) ALPINE - High TREELINE - High BELOW TREELINE - Considerable TRAVEL ADVISORY: If more snow than is forecast arrives, expect the danger to increase in proportion to the amount of snow occurring. The activity stepping to the November facets in the Purcells indicates the entire region may be poised for a major full depth avalanche cycle, with the amount of snow and wind arriving early in the weekend being the deciding factor. The avalanche danger may be most pronounced near treeline. ROCKIES REGION WEATHER: Some snow arrived once again, with up to 15cm of storm snow added to the alpine by Thursday. Temperatures remained warm, and moderate, gusty winds blew out of the West. The forecast calls for a bit more snow early in the weekend, winds climbing to 50km/hr in the alpine, then a clearing trend for the weekend. Winds should drop by later Saturday, and temperatures will cool down. SNOWPACK: A wind slab which developed mid week will grow fatter if the weather forecast materializes as predicted. A surface hoar layer found about mid snowpack may once again come to life now we have some new snow. The base of the snowpack is weak and composed of facets and depth hoar. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (Feb 5th) ALPINE ^Ö Considerable, trending to high with wind loading TREELINE - Considerable, trending to high with wind loading BELOW TREELINE ^Ö Moderate AVALANCHES: Naturals to size 2.5 began mid week, and human triggered slides were frequently reported as well. One slide stepped to ground when it ran to treeline, where wind loading was more pronounced. TRAVEL ADVISORY: The wind may be making a significant contribution to rising danger, despite the fact storm snow amounts may be only 20cm by the weekend. This is an unusually shallow and eggshell snowpack, and 50 km/hr winds accompanied by new snow may overwhelm the stiffer supporting layer found mid snowpack. Anything that runs even to size 1 may step to ground. One positive aspect about this winter is that the alpine north faces are often still clear, beautiful ice, and many ridges are wind blasted to bare rock, so this season might offer some winter ascent possibilities if you can approach and get off without having to be exposed to avalanche terrain.