Nature and possible causes of droughts on the canadian prairies‐case studies

There has been increasing interest in recent years in the study of droughts because of their economic, social and political impacts on society. Two summer droughts that affected the Canadian Prairies in 1961 and 1967 are examined. Based on a synoptic climatological approach, the investigation reveals that droughts occurred when the weather type WR (mid‐tropospheric ridge dominant) was persistent with a ridge over western Canada. A study of the 1976–1977 winter drought supports this interpretation. In all three cases, a quaststationary mid‐tropospheric ridge over western Canada acted as a block which displaced the jet stream, cyclones and moist air masses to a location north of the Canadian Prairies, while anticyclonic circulation under the high pressure ridge gave atmospheric stability and dry conditions on the Canadian Prairies.