Surface Meteorological Observations of Upslope Cyclonic Precipitation Events in the Eastern Slopes of the Canadian Rocky Mountains

In June 2005, four multi-day cyclonic storm events, each characterized by easterly upslope advection and orographic uplift, passed over southern Alberta, Canada. The low pressure systems stalled in the region, giving persistent cool, wet conditions punctuated by several days with heavy rains. These storms caused extensive flooding in southern Alberta, where 14 municipalities declared states of emergency, and over 40 reported significant infrastructure damage. The dates of these storms and the maximum accumulated rainfall in the region were: 1-5 June (140 mm), 5-9 June (240 mm), 16-19 June (150 mm), and 27-29 June (90 mm). This presentation examines surface meteorological observations during these precipitation events. Research was undertaken as part of the Foothills Climate Array (FCA), a network of 280 meteorological stations (each containing a tipping bucket and temperature/humidity sensor) set up in 2004-2005 to study mesoscale climatological processes in southwestern Alberta. The FCA network begins at the continental divide, traversing the eastern slopes of the Rocky Mountains and ending in agricultural lands approximately 50 km east of the city of Calgary. Five fully equipped automatic weather stations, embedded within the array, provided supplemental observations. Data from FCA stations suggests that the spatial organization of the surface rainfall was strongly influenced by the orography of the underlying surface and the freezing levels in higher elevation sites. The most intense precipitation of these four rainstorms occurred along the foothill area east of the Rocky Mountains, where the topographic lifting is strong. Additional analysis of these storm events compared to long-term normals was performed. Precipitation in June 2005 established new 24-hour and one month totals in most of the region. On average 2005 totals were 409% of the climate normals.