Technical Abstract: Can long-term (1919 to 2000) winter wheat yield trends in Oklahoma be explained by climate variability? Winter wheat yields from eight counties were compared to seasonal trends in precipitation and temperature. Seasonal values were computed by summing the precipitation, and averaging the mean daily temperature, over 3-month periods: Summer (June-September), Fall (October-November), and Winter (December-February). Seasonal precipitation and temperature anomalies were computed by subtracting the long-term seasonal average from each yearly seasonal value and dividing by the long-term standard deviation. An Aridity Index (AI) was expressed as the difference between the temperature and precipitation anomalies. The Southern Oscillation Index (SOI) values were averaged on a seasonal basis. Winter wheat yields increased in a non-linear fashion and the data were fitted with a sigmodal equation. Yield data were expressed as a ratio of the deviations to the predicted yields. Based on average SOI values for a crop year wheat yields were higher in EL and neutral (N) years and lower in LA years. This trend was reflected in the precipitation and temperature anomalies: precipitation was greater, and temperature cooler, in the EL and N years as compared to LA years. The AI showed less arid conditions during EL and N years and more arid conditions during LA years. Overall, the AI value broadly reflects the variability in the wheat yield trends.