Variations in growing conditions and genotypic influences are the main factors affecting wheat processing quality in western Canada. Environmental variables such as useful heat accumulation, heat stress and moisture stress influence the rate and duration of wheat grain development and protein accumulation, leading to considerable variation in yield, protein content and protein yield in wheat grown across the Canadian Prairies. Genotype also plays a significant role in yield, protein content and protein yield variation. The overall understanding of the relationships between specific weather parameters and genotype by weather interactions on wheat quality is quite limited. A quantification of the relationship between wheat processing quality parameters and weather induced stress is needed to help understand wheat quality variability that arises within a genotype but between growing seasons. Six commercial wheat cultivars were grown in five locations across the Canadian prairies over two years. Intensive weather data was collected during the growing season at each location and used to calculate accumulated heat stress, useful heat and moisture stress for numerous crop development stages. Analysis of variance indicated a significant difference (P<0.001) among environments as well as among cultivars for grain properties including grain yield, protein content and protein yield. Yield, protein content and protein yield variation between environments was 380%, 55% and 315% respectively, while variation among genotypes was only 34%, 14% and 17% respectively. This tremendous variation between environmental and genotypic influences clearly demonstrates the importance of growing season weather impacts on wheat yield and quality.