(WXIN) — While fall begins on Sept. 22, leaf peepers in most parts of the United States will have to wait a few weeks until peak foliage time, according to one prediction map.

The Smoky Mountains are one of the most popular places to catch leaves changing color, and its 2022 Fall Foliage Prediction map is a tool designed to help travelers decide on the best time to visit.

Using a complex algorithm, the map forecasts county-by-county fall foliage based on millions of data points. The data includes historical temperatures, historical precipitation, forecast temperatures from the National Oceanic and Atmospheric Administration; historical leaf peak trends, and even user-generated information.

The northernmost states in the contiguous U.S. are the first to see the changing of leaves, and the trend slowly trickles down to the southernmost states.

Across the U.S., the peak foliage happens sometime between Oct. 3 and Nov. 21.

For Smoky Mountain visitors, the leaf peeping doesn’t get better than the week of Oct. 31.

In the Midwest, the second and third weeks of October are typically the peak times, depending on your location, according to the Almanac. The change there starts by late September.

In the New England area, also beloved for its colorful fall leaves, peak foliage will be around Oct. 10, according to the foliage prediction map.

Why do leaves change color?

Chlorophyll is the compound that gives leaves their green color and helps plants by converting sunlight into “food” through photosynthesis.

As the days get shorter and colder in the fall, chlorophyll in leaves breaks down and reveals the natural colors underneath, including red, orange and yellow.

The colors are based on chemicals in the leaves like carotenoids and anthocyanin, according to the Harvard Forest.

What’s the effect of the weather?

“Another important part of leaf-peeping is knowing the right time to go!” according to the Almanac. “For the best experience, not only should leaves be near their peak colors, but the weather should be agreeable, too.”

While many folks prefer blue skies and full sun to view the brilliance of the changing colors, others say a lightly overcast day could make the colors appear to “pop against the somber skies.”

The least desirable conditions are rain and wind, the latter of which can result in prematurely bare trees, the Almanac said.