Temperatures warmed into the mid and upper 60s across the western Dakotas on Monday. As this weather blew into the eastern Dakotas and Minnesota on Tuesday, it was considerably cooler. Such is often the way with Chinooks. The term is actually the tribal name of a group of Native Americans from the Columbia River region of Washington and Oregon, but also refers to a warm wind blowing down from the Northern Rockies.
The key to a Chinook wind is the change in temperature associated with the change in air density. Specifically, moisture-laden air moves up and over the western side of the Rockies, cooling as it rises, and expending much of its water vapor as rain and snow. Dropping down into the High Plains, the now dry air warms up faster than it cooled. Farther east, the lack of slope reduces this effect. We get milder air, but not so extraordinarily warm as out west.