February 2, 2004 This Forecast Sponsored by Canadian Pacific Railway. South Coast Region Weather: The weather will be cloudy with light snow Monday through Tuesday. Accumulations in alpine areas should be 5-10 cm for the period, tapering off to flurries on Wednesday. Winds are forecast by the Meteorological Service of Canada to be light from the NW shifting gradually to light from the S by Tuesday. Snowpack: In alpine and treeline areas a variety of windslab layers are reported on the surface of the snowpack. Recent winds have been from various directions so slabs are known to exist on all aspects. 50-100 cm below the surface a layer of facets persists, occasionally the facets are associated with buried surface hoar. This layer sits on a rain crust below 2200 m and on a wind crust above. Stability tests on this layer are variable indicating that it is gaining strength in some places but may not be in others. In a thinner snowpack area a human triggered avalanche yesterday stepped down to the facet layer at the base of the snowpack reminding us in dramatic fashion that this layer persists. Avalanche Activity: A few significant human triggered avalanches were reported on Sunday. These avalanches were associated with windslab layers initially, but as mentioned above at least one stepped down becoming a large deep avalanche. Looking ahead, human triggered avalanches are still likely on the windslab layers or on facet weakness 50-100 cm below the surface. Forecast of Avalanche Danger Up To Wednesday Evening (February 4, 2004) Alpine ^Ö CONSIDERABLE Treeline ^Ö CONSIDERABLE Below Treeline ^Ö MODERATE Travel Advisory: The key feature of the snowpack is variability. Some areas are reporting that the storm snow and the windslab layers are well bonded. In other areas such as along the Duffy Lake Road the snowpack is still reported to be touchy. An important consideration is that larger triggers, such as a snowmobile may be able to trigger an avalanche where lighter triggers did not. Sledders are advised to maintain a cautious approach to steeper terrain. North Columbia Region Weather: Cool alpine temperatures and clear skies overnight on Sunday have caused a layer of surface hoar to form. Weather should remain slightly cooler than seasonal norms, but clouds will move in overnight on Monday preventing really frigid conditions from developing. Flurries will give us 5 cm of snow in alpine areas on Tuesday, tapering off on Wednesday. Light winds will shift gradually to the SW by Wednesday afternoon. Snowpack: Storm snow has settled well in areas where no slab formed. A weak layer is widely reported in the storm snow 40 cm below the surface. This layer gives moderate to hard scores on stability tests, and should still be considered to be ripe for triggering where it is overlain by a soft or hard slab. A layer of surface hoar 70-100 cm exists in some locations but not others, where seen it can be released by human triggers. Avalanche Activity: Sizeable natural avalanches were observed on Monday, some were associated with solar heating of south aspect slopes. Several sizeable human triggered avalanches were observed on Sunday on storm snow layers, and at least one human triggered avalanche occurred Monday on the buried surface hoar layer. Forecast of Avalanche Danger Up To Wednesday Evening (February 4, 2004) Alpine ^Ö CONSIDERABLE Treeline ^Ö CONSIDERABLE Below Treeline ^Ö MODERATE Travel Advisory: The main danger is encountering slab conditions. Where the slab is absent the storm snow is settling well, but in alpine and treeline areas there is still the likelihood that windslabs can be triggered by human activity. Sun shining on S facing slopes can release large avalanches travelling long distances. South Columbia Region Weather: Weather should remain slightly cooler than seasonal norms, but clouds and light snow Monday afternoon should prevent really frigid conditions from developing. Flurries will give us 5 cm of snow in alpine areas on Tuesday, ending Wednesday. Winds will be generally light and shift to the SW by Wednesday afternoon. Snowpack: Three weak layers within the storm snow were observed in stability tests Sunday the most consistent of these was a layer down 50-65cm giving moderate test scores indicating that triggering of this layer is still possible. A significant layer of surface hoar is buried anywhere from 30 to 100 cm deep, and was observed to be responsible for explosive triggered avalanches in the Purcells. Where the snowpack is shallow a layer of facets or depth hoar near the base of the snowpack persists. On the surface, a sun crust is forming on southerly aspects, and surface hoar elsewhere. Avalanche Activity: Explosive charges triggered large avalanches on Sunday and Monday in the Purcell Mountains. Many were seen to run on a layer of surface hoar buried 40-100cm deep. A few avalanches stepped down to a facet layer near the ground reminding us of the persistence of this layer where the snowpack is thin. Forecast of Avalanche Danger Up To Wednesday Evening (February 4, 2004) Alpine ^Ö CONSIDERABLE caution in windslab areas of the Purcells.* Treeline ^Ö CONSIDERABLE Below Treeline ^Ö MODERATE Travel Advisory: It is a good time to be cautious in the Purcells. Low snowpack areas like Quartz, Gorman, Holt and Lang creeks (in particular, but also others like them) are likely to have slabs that could be triggered by human activity. Spacing out in terrain threatened by avalanches from above, and gathering in spots not exposed to avalanche runouts are ways to reduce risk in avalanche terrain. Be increasingly cautious in steeper terrain. Kootenay Boundary Region Weather: Weather should remain slightly cooler than seasonal norms, but clouds and light snow will move in on Monday afternoon preventing really frigid conditions from developing. Flurries will give us 5 cm of snow in alpine areas on Tuesday, tapering off on Wednesday. Winds will be generally light and shift gradually to the SW by Wednesday afternoon. Snowpack: Cool alpine temperatures and clear skies overnight on Sunday have caused a layer of surface hoar to form. Windslabs exist in many alpine and treeline areas. Stability tests continue to identify weak layers within the recent storm snow. A layer 40-60cm below the surface has moderate to hard test scores indicating continued potential for human triggering. Another layer 80-120cm deep has been identified; hard stability test results are reported indicating some strengthening has occurred. A layer of surface hoar 100-150cm below the surface remains very significant. *On southerly aspects, this surface hoar layer sits on a crust and is now deep enough to produce very large avalanches. Avalanche Activity: Only sluffing of new snow layers was reported on Sunday, however human triggering of avalanches in alpine and treeline areas is still likely given the highly variable nature of the upper snowpack. Cooler temperatures have strengthened the snowpack below 1600m. Forecast of Avalanche Danger Up To Wednesday Evening (February 4, 2004) Alpine ^Ö CONSIDERABLE Treeline ^Ö CONSIDERABLE extra caution advised on south aspect slopes* Below Treeline ^Ö MODERATE Travel Advisory: While triggering of avalanches may be becoming less frequent, the consequences of triggering an avalanche remain high. Larger triggers such as a sled could release deep avalanches or could release avalanches where lighter triggers did not. South Rockies Region Weather: Winds from the E and N Monday should shift around to the SW on Tuesday remaining moderate or light. Cloudy skies and flurries are expected for Tuesday and into Wednesday. Snowfall should be light with just a few cm accumulating. Temperatures are expected to be cool and getting cooler by Wednesday morning. Snowpack: Reports indicate that the storm snow is strengthening. 3 moderate to hard shears are reported in the storm snow indicating that these layers are strengthening. In a shallower snowpack area the snowpack was observed to be 50 cm of storm snow over a facetted base. Moderate stability test scores on the old snow surface indicate that there is potential for human triggering of this layer. Avalanche Activity: Natural avalanche activity was not observed on Sunday. Explosives triggered one small avalanche within the storm snow. Triggering of avalanches will be more likely in areas with a low snowpack. Sun shining on southerly slopes could trigger large avalanches running long distances. Forecast of Avalanche Danger Up To Wednesday Evening (February 4, 2004) Alpine ^Ö CONSIDERABLE Treeline ^Ö MODERATE areas of CONSIDERABLE* Below Treeline ^Ö MODERATE Travel Advisory: Avalanche danger is not uniform throughout the area. *Where the alpine snowpack is thin, say 150 cm or less, expect danger to be CONSIDERABLE. Our reporting network is limited outside the snowbelt area around Fernie, so a cautious approach to avalanche terrain is recommended in these areas. A larger trigger such as a snowmobile could release deep avalanches or could release avalanches where lighter triggers did not. Issued by: jk