I'm watching the monsoon rains come up on a rain radar from Sonora and Chihuahua states of Mexico

 Mostly likely they are coming off the Pacific Ocean or Gulf of Mexico or Gulf of California in Baja California. But, then they are traveling north as far as Montana and North and South Dakota before they head eastward mostly. Likely some of the rain and snow we saw in the Tetons. and Yellowstone and Banff and Lake Louise were also from this same monsoon rain pattern I'm seeing now too.