Grasshoppers have been a chronic problem for agriculture on the Canadian prairies, the northern limits of the Northern Great Plains, since settlement of the region in the mid-1800s. Grasshopper pest management tools include biological control, cultural control, and insecticides. This article describes a mechanistic, or process-based, modeling approach used to assess the development and abundance of the migratory grasshopper, Melanoplus sanguinipes (Fabricius), based on a complex of environmental drivers. The purpose of the study was to develop and validate a model (using extensive field data) to quantify the effects of interannual weather variation on M. sanguinipes development and abundance in Saskatchewan, Canada. Overall, the accuracy of model predictions improved for later instars and adults such that predictions regarding adult populations were highly similar to field-collected data. The model provides greater understanding of how M. sanguinipes oviposition is related not only to adult densities, but also to the first appearance of adults and to weather conditions during the oviposition period. The model output can be used to provide accurate within-season updates of the status of grasshopper populations in western Canada to optimize pest management.