March 19, 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. SOUTH COAST REGION WEATHER: After slowly deteriorating weather, a very significant storm rolled through the region Sunday night, bringing heavy rain below treeline, and dropping up to 25cm of heavy snow in the alpine. Winds were reported holding steady at 70km/hr during the storm, with gusts hitting the 100km/hr mark. Monday, temperatures dropped below freezing as the storm ended, and winds abated. The forecast calls for unsettled weather, with a rising freezing level and the chance of rain or snow each day. SNOWPACK: The storm came in warm, even in the alpine, and bonding with the old snow surface was reasonable. The heavy winds stripped snow from exposed areas and deposited a winds slab in lee areas, leaving behind a highly variable alpine snowpack. The rapid loading has stressed several buried surface hoar layers in the upper 100cm, which were again giving easy to moderate shears in snowpack tests, especially on north aspects. Below treeline, the surface is a short lived crust, with wet, weak, near isothermal snow to ground under that. AVALANCHES: During the storm, a widespread cycle of moist naturals were observed treeline and below. This activity temporarily ended as temperatures dropped. The wind and loading in the alpine produced a round of natural slab releases, and the occasional deep release to buried surface hoar weaknesses. Monday, explosive testing in the alpine was still easily triggering wind loaded pockets of slab left over from the storm. FORECAST OF AVALANCHE DANGER UP TO THURSDAY EVENING (Mar 22nd) ALPINE - Considerable TREELINE - Considerable BELOW TREELINE ^Ö Considerable, deteriorating if significant rain occurs TRAVEL ADVISORY: Cornice fall will be frequent in the coming days, and this may be the trigger necessary to wake up the November facet layer as we move toward spring. NORTH COLUMBIA REGION WEATHER: The weekend added another half metre of snow to the alpine, although we paid the price below treeline with heavy rain all Sunday night. Winds were averaging 50km/hr out of the south by Monday, as the snowfall tapered off. The weather forecast calls for cold air to invade out of the north, affecting the north half of the region. Throughout the region, conditions will be generally dry, with a mix of sun and cloud. SNOWPACK: The rain line rose to approximately 200m below treeline Sunday night. Wind slab was evident in most exposed areas in the alpine and treeline by Monday, with a crust on the surface below treeline. The various buried surface hoar layers in the upper 150cm continue to be stressed by the sustained loading which has occurred in the last week. The most troublesome weakness continues to be a buried surface hoar layer down 50-75cm (100-125 near Valemount), particularly on northerly aspects. Below treeline, the march toward spring continues. AVALANCHES: The occasional storm snow and buried surface hoar failure was reported, including one human triggered event in the alpine that claimed the life of a skier near Revelstoke. As temperatures climb above zero, expect the tendency for human triggering to rise as well. FORECAST OF AVALANCHE DANGER UP TO THURSDAY EVENING (Mar 22nd) ALPINE ^Ö Considerable, areas of High TREELINE ^Ö Considerable, areas of High BELOW TREELINE - Considerable TRAVEL ADVISORY: The cooler weather will improve stability somewhat, but any trend to above zero temperatures will reverse this condition. SOUTH COLUMBIA REGION WEATHER: Sunday^Òs storm left behind up to 30cm of snow in the alpine, which was followed up by strong winds on Monday as the snowfall tapered off. Below treeline, light rain was reported Sunday night. The weather forecast calls of a general drying trend, with a mix of sun and cloud through mid week. . SNOWPACK: In the alpine, a sun crust under the storm snow was causing easy shears on southerly aspects. The winds transported snow into lee pockets and left wind slabs around terrain features. Below treeline, the rain caused further deterioration in snowpack strength as more heat was pulled down into the lower layers. This condition is temporarily hidden under a crust, although a return to warmer temperatures will break this down. The entire South Columbia snowpack is beginning to show signs of loosing strength with recent solar heating and above zero air temperatures. AVALANCHES: Most events reported have been alpine slabs up to size two released by ski cutting on steep terrain features. Pockets of wind slab will continue to show potential for this. FORECAST OF AVALANCHE DANGER UP TO THURSDAY EVENING (Mar 22nd) ALPINE - Considerable TREELINE - Moderate BELOW TREELINE ^Ö Moderate, deteriorating with afternoon heating TRAVEL ADVISORY: Watch for overnight lows remaining above zero, which will signal accelerated snowpack deterioration due to heating. Lower elevation areas in the south are beginning to loose snow entirely on solar aspects. ROCKIES REGION WEATHER: The storm which hit the BC Interior Sunday had arrived in the north central Rockies by Monday, with observers reporting heavy cloud build up, rising winds, and light rain in upslope areas. The weather forecast calls for snow in the alpine and rain at low elevations, both accompanied by strong winds. The storm track is northward, so more moisture is expected further north than in the south Rockies. SNOWPACK: In the Columbia Icefields area, heavy snow had developed by Monday, bring the storm snow total to around 50cm. This amount gets progressively less further south along the Rockies until virtually no snow was reported near Waterton Lakes. The storm snow is heavily wind affected, with additional loading stressing the entire snowpack where it has been deposited in lee slopes and around terrain features in the alpine. The low elevation rain has pretty well finished the snowpack near valley bottom. AVALANCHES: Some low elevation activity was reported Saturday, failing occasionally to ground at size 2.5 or less. No activity of note has been reported to Monday, although the wind and snow in the weather forecast is expected to change this. FORECAST OF AVALANCHE DANGER UP TO THURSDAY EVENING (Mar 22nd) ALPINE ^Ö Considerable, High if heavy snow and wind occur TREELINE ^Ö Considerable, High if heavy snow and wind occur BELOW TREELINE - Moderate TRAVEL ADVISORY: Keep an eye on what the storm delivers Monday night and Tuesday. Significant moisture loading will stress the fragile snowpack into rapid deterioration.