February 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: Winds remained light, temperatures continued to grow milder, and with the longer days of late February, talk of spring was in the air. Sunday, a disturbance tracked through, leaving behind 15cm of light snow in the alpine. The weather forecast calls for a ridge of high pressure to continue to build, with a possible breakdown near the end of the week. Weather forecasters indicate there is not complete confidence the ridge will continue to build, warning folks that there is some possibility of heavy snow later in the week if the two low pressure systems offshore Monday prevail instead. SNOWPACK: The new snow was light and fluffy, so despite the fact winds remained light, some loading into lee features occurred. Several buried surface hoar layers in the upper 50cm are still reactive, with the uppermost often reported as an easy shear in snowpack tests. The midpack is relatively strong still in all but shallow areas. The base continues to be the November facets. AVALANCHES: Ski cutting would trigger the new snow or wind loaded pockets to slide. Solar radiation may produce some naturals on south facing aspects mid week. FORECAST OF AVALANCHE DANGER UP TO THURSDAY EVENING (Feb 22nd) ALPINE - Moderate TREELINE ^Ö Moderate BELOW TREELINE - Low TRAVEL ADVISORY: Adjust these ratings upward if the heavy snow scenario materializes, with the danger rising in proportion to the amount of snowfall occurring. NORTH COLUMBIA REGION WEATHER: After starting the weekend sunny and warm, a front moved in Sunday and brought low density powder snow to all elevations. By midnight Sunday, snows stopped, with up to 20cm in the alpine, and the ridge of high pressure started to rebuild. This is likely to continue till late in the week, although weather forecasters indicate that several possible weather pictures may happen this week, including the possibility of heavy snow mid week from two low pressure systems out in the Pacific. Warm and pleasant is the strongest possibility though, with the ridge diverting the lows both north and south of the Columbia ranges. SNOWPACK: The surface snow was light and low density, and came in with virtually no wind. Up to three buried surface hoar layers are found in the upper metre of the snowpack, and these continue to be identified as failure planes in snowpack tests. Below the midpack layers sit the November facets, weak but inactive right now in all but shallow areas. AVALANCHES: Ski cutting on steep terrain will still produce failures on the buried surface hoar layers, usually failing down 30 or 80cm depending on the layer. Treeline appears to be the most active zone. Worth noting are several reports of human triggered slides failing on old bed surfaces from avalanches that ran earlier in the winter. Usually, these releases are on surface hoar formed on the bed surface and then buried, or a layer of facets just above the bed surface. FORECAST OF AVALANCHE DANGER UP TO THURSDAY EVENING (Feb 22nd) ALPINE ^Ö Moderate, areas of High TREELINE ^Ö Considerable, Areas of High BELOW TREELINE - Moderate TRAVEL ADVISORY: As the weather warms up, watch for cornice fall triggering a slide. If the weather turns to snow, adjust these ratings upward in proportion to the amount of snow arriving. SOUTH COLUMBIA REGION WEATHER: A low tracking onshore in the US kept skies cloudy for most of the weekend, but the sun poked through on occasion. By Sunday, most areas had still received less than 10cm of new snow. The weather forecast calls for a ridge of high pressure to continue to build over the BC interior till late in the week. The weather right now is quite unpredictable, and weather forecasters warn that two lows out in the Pacific Thursday may prevail, perhaps delivering some moderate snowfalls instead. SNOWPACK: The new snow was light and fluffy, but with the absence of wind did not move around much. In the north parts of the area, where less cloud occurred, the new snow is poorly bonded to a pronounced sun crust on south facing aspects. Mid snowpack, up to three layers of buried surface hoar can still be identified in the top 100cm. Below this sit the weak but right now predominantly inactive November facets. AVALANCHES: Heli bombing in the south produced one size 3 and a few smaller releases. All other areas report limited activity, usually surface sluffing in steep terrain. FORECAST OF AVALANCHE DANGER UP TO THURSDAY EVENING (Feb 22nd) ALPINE - Moderate TREELINE - Moderate BELOW TREELINE - Low TRAVEL ADVISORY: If the low pressure systems do prevail and snow develops, adjust these danger ratings upward in proportion to the snow occurring. Avalanche rescue equipment is showing up in spring sales as retailers make room for summer stock, so if you or someone you know is still not equipped with a beacon, probe, and shove, now may be the time to get equipped for spring backcountry touring season. ROCKIES REGION WEATHER: Although the weekend started with seasonal temperatures, things warmed up quickly on Sunday as a front moved through, leaving behind up to 10cm of light, low density powder. The weather forecast calls for a ridge of high pressure to continue building, giving sunny weather until Wednesday, when cloud will move in, with a chance of snow to follow. Winds will pick up as the cloud moves in. There is a possibility that heavy snow may develop late in the week, which was still difficult for weather forecasters to predict on Monday. SNOWPACK: The new snow was light and added very little weight onto the still fragile midpack layers. The lower snowpack is still entirely facets and depth hoar, weak but inactive at this point in most areas. AVALANCHES: Explosive testing and control work was carried out in many areas Monday, and the surface layers came off steep slopes reliably. Very little has been reported recently for natural activity. FORECAST OF AVALANCHE DANGER UP TO THURSDAY EVENING (Feb 22nd) ALPINE - Considerable TREELINE ^Ö Considerable BELOW TREELINE - Moderate TRAVEL ADVISORY: If heavy snow does arrive, expect the danger to jump to High very rapidly. Solar heating will be subtly weakening midpack strength on steep south aspects, so keep an eye on changes on these slopes this week.