How does rainfall change from east to west across the Great Plains?

Across the Great Plains, the climate becomes progressively drier as you move from east to west.1

The primary source of moisture for the region is the Gulf of Mexico, and precipitation levels decrease as distance from this source increases. For example, the eastern margin of the plains in Nebraska receives approximately 25 inches of rain annually, while the western margin in Montana receives less than 15 inches. This gradient in moisture also influences the region's mollisols, as the depth of carbonate accumulation in the soil decreases alongside the reduction in rainfall.1