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This data-driven, interactive map helps users determine what the foliage color will be like on a given date this fall. (smokymountains.com)

When is the best time to see fall color across Alabama this year? One of the most popular prediction maps says it knows county-by county not only across Alabama, but across the United States. In Alabama, the site says most of the state will be nearing peak color the week of Oct. 21 and peaking the week of Oct. 28.

The map was created by the website smokymountains.com, which acknowledges precise predictions are hard given the multiple factors at play. But the site believes it has built a map "that's useful, fun and accurate." You can also see it below.

Media sites seem to agree: This will the second year the map is featured on Travel+Leisure, and it has been featured on Mashable and Business Insider.

"To create the map, we create a foundational data set that includes a conglomeration of NOAA precipitation forecasts, daylight and temperature forecasts, historical precipitation data for the current year, and aggregated information from the many government and private party data sources available online," said map engineer Wes Melton.

Why do leaves change color in the fall? It's because shorter days and less sunlight signal the green chlorophyll in them that it's time to stop their summer job of producing food and begin to break down. That lets the other colors present in leaves all along - yellows, reds and purples - shine through.