Large-scale atmospheric circulations and anomalies have significant influence upon seasonal weather over many parts of the world. We examined the impact of sunspot activity and large-scale atmospheric features on regional seasonal weather, as well as implications for crop yield and agronomy. The atmospheric variables analyzed included the stratospheric quasi-biennial wind oscillation (QBO), El Niño/Southern Oscillation (ENSO), and North American snow cover (NAS) on Canadian summer rainfall, regarded as a key variable for establishing grain yield. Because the study is an exploratory one, we focused on correlation coefficients between selected variables. The analysis is based on 55 yr of atmospheric, crop yield and climatic data for > 50 weather stations over the Canadian Prairie region. Our study reveals that high (low) sunspot activity, an easterly (westerly) phase of the QBO, persistent La Niña (El Niño) conditions and heavier (lighter) than normal NAS in seasons leading up to the summer months are associated with low (high) summer rainfall. KEY WORDS: Summer rainfall · Snow cover · Sunspots · ENSO · QBO · Canadian Prairie · North America Resale or republication not permitted without written consent of the publisherClim Res 32: 25-33, 2006, Shabbar et. al. 1997, Garnett et. al. 1997, 1998, Hsieh et al. 1999, Garnett 2002. This condition favors spring wheat yield. Conversely, when SSTs in the central and eastern equatorial region of the Pacific Ocean are below normal during winter and early spring (that is, a prevailing La Niña), precipitation over the Canadian Prairies during the months of June and July is below normal. Consequently, wheat yields are reduced. Garnett (2002) found that statistical relationships with ENSO were strongest in Saskatchewan's brown soil zone in the southwest part of the province and weakest in the black soil zone in the northeast part of the province. In short El Niño is a friend and La Niña a foe to spring wheat growing in the Canadian Prairies.Among many other large-scale atmospheric features, the sunspot cycle, as a determinant of regional seasonal weather conditions, has received attention from a number of researchers. The Max Planck Society (press release, October 28, 2004; available at http:// www.mpg.de/english/portal/index.html) puts forth the mechanism by which sunspot activity may affect precipitation. Sunspot activity and cosmic ray intensity are inversely correlated, and therefore during periods of high (low) sunspot activity cosmic ray intensity diminishes (increases). Ions produced by cosmic rays act as condensation nuclei for a larger suspension of particles and thus contribute to cloud formation. With increased solar activity (and stronger magnetic field) the cosmic rays decrease and with it the amount of cloud coverage, resulting in a rise of temperatures on the earth. Conversely, a reduction in solar activity produces lower temperatures. Thompson (1973) pointed to the effects of the double sunspot cycle on the USA Corn Belt and middle latitudes. Currie (198...