The freeze-free season is expected to increase by 15 to 33 days in the Northern Great Plains by the middle of the century.

The freeze-free season is defined as the period of time between the last spring frost (daily minimum temperature below 32 degrees F) and the first fall frost. The length of the annual freeze-free season has been increasing since the 1980s, and all climate models agree that it will continue to increase in the future. The largest increases are projected for the high country of Wyoming and Montana.