March 15, 2001 This Bulletin Sponsored by Marmot Gear 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. SOUTH COAST REGION WEATHER: After a ridge of high pressure cleared skies for the middle of the week, a system moved onshore Thursday, bringing a return to wind and rain, with wet snow in the alpine. The weather forecast calls for a brief reprise Friday, then a more significant low pressure will flow out of the Gulf of Alaska by Saturday morning. The alpine is predicted to get steady snow and moderate to strong winds into the beginning of next week. SNOWPACK: The storm snow accumulation was in the range of 20-30cm by Thursday. This is sitting on various crusts on south aspects, although the bond appears to be reasonable between the two layers. Many protected areas, particularly on north aspects, have a layer of surface hoar buried about 40cm down, which is reactive in snowpack tests. As the new snow settles into a slab, this layer may become more likely to propagate into larger avalanches. The low elevation snowpack is deteriorating due to rain and heat, and this will continue. AVALANCHES: Numerous storm snow avalanches to size 2.5. Some human triggered events, particularly on north aspects. With more snow loading in the forecast, the potential for failure will be sustained. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (19th) ALPINE ^Ö Moderate, areas of Considerable TREELINE - Considerable BELOW TREELINE - Moderate TRAVEL ADVISORY: The surface hoar reported buried down 40cm is variable in distribution, so keep an eye out of it in open breaks near treeline and on north facing shaded bowls. Check out the link to the interactive discussion board on the South Coast bulletin page at www.avalanche.ca. NORTH COLUMBIA REGION WEATHER: Rather pronounced variation in weather occurred this week, with up to 120cm of storm snow falling near McBride in just a few days, while further south storm snow amounts were only about half a metre. Strong winds affected the alpine throughout the region. A ridge of high pressure formed Wednesday to clear skies, but by Thursday afternoon, weather was deteriorating again as a Gulf of Alaska low rolled toward the region. By Saturday, snow and wind is predicted to be once again affecting upper elevations, with rain below. SNOWPACK: The storm snow is wind affected in exposed alpine areas, and solar radiation has stiffened the surface on south aspects. North aspects have a layer of surface hoar buried just under the storm snow interface, which can be down approximately 60cm near Revelstoke, and about 140cm down near McBride. This layer remains the principal weakness in the alpine snowpack in most areas. The low elevation snowpack has deteriorated seriously due to solar radiation and extensive rainfall in recent days. AVALANCHES: Naturals and human triggered events continue to be reported, ranging in size up to 3.5. Virtually all are failing at the storm snow interface or the surface hoar layer buried just below. With more wind and snow in the forecast, this potential could persist throughout the weekend. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (19th) ALPINE ^Ö Considerable, areas of High TREELINE ^Ö Considerable, areas of High BELOW TREELINE - Considerable TRAVEL ADVISORY: Long term research has proven that March is the month of the year most likely to produce avalanche tragedies. For more specific information on conditions, try checking out the interactive discussion board for the North Columbias, by going the North Columbias bulletin page and clicking on the discussion link. Post a question or let people know what you have observed yourself. SOUTH COLUMBIA REGION WEATHER: Although a series of cloudy days interspersed with sun characterized the week^Òs weather, very little snow or rain resulted. The alpine had 75km/hr winds out of the SW on Tuesday, although this died down later in the week. A ridge of high pressure built for Thursday, clearing skies briefly. Clouds and wind are forecast to return for late in the weekend. SNOWPACK: Although some new snow arrived in the alpine early in the week, in the Kootenays the wind stripped that from all exposed areas, leaving behind the old crust from last weekend. About 35cm of storm snow fell in the Monashees by Thursday, with less severe wind affect as well. North aspects have a surface hoar layer buried about 50cm. All areas report the low elevation snowpack as weak, isothermal, and not fun! AVALANCHES: Scattered activity to size 2.5, failing at the storm snow crust interface on sunny aspects, or a buried surface hoar layer just below on north aspects. Triggers were natural and human, including remote releases. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (19th) ALPINE - Considerable TREELINE - Moderate BELOW TREELINE - Moderate TRAVEL ADVISORY: Looking for more specific information? Check out the discussion board on the CAA website, and click to the South Columbia bulletin page. You will find a link there which leads to a discussion board, where you can post questions or let others know about conditions you have found in the backcountry. ROCKIES REGION WEATHER: This week brought a welcome addition to the snowpack, with up to 15cm of snow added in the alpine. Unfortunately, strong winds stripped this from exposed slopes, loading cross wind terrain features and lee slopes. By Thursday, more reasonable weather had returned under the influence of a ridge of high pressure. The weather forecast calls for this to decay on the weekend, with increasing cloud, and a chance of further snowfall. SNOWPACK: The snowpack surface varies, with wind blasted crust in exposed slopes, some dry powder in sheltered and lee slopes, and weak isothermal snow at low elevations, particularly in the trees. The midpack has been steadily loosing strength, to the point where now even small avalanches are easily stepping into the lower snowpack or going to ground. The base is the November facets and associated depth hoar. AVALANCHES: Regular human and explosive triggered activity to size 3, often stepping to ground. A close call near Golden in the alpine, with out of bounds skiers getting a size 3 going, luckily without tragic consequences. Further south near Fernie, less activity has been observed but explosive testing reliably produces small releases here as well. FORECAST OF AVALANCHE DANGER UP TO MONDAY EVENING (19th) ALPINE ^Ö Considerable TREELINE - Considerable BELOW TREELINE - Moderate TRAVEL ADVISORY: Looking to find out more about a certain area or particular snowpack problem? Check out the interactive discussion page on the CAA Rockies bulletin page at www.avalanche.ca. Click on the discussion link, and post a question or better yet, your observations from the field after you return from a trip.