PORTLAND, Maine (AP) — Fall is back, and bringing with it jack-o'-lanterns, football, pumpkin spice everything and — in some parts of the country — especially vibrant foliage.

Leaves around the northern U.S. are starting to turn orange, yellow and red, inspiring legions of leaf lovers to hop in their cars and travel to the countryside for the best look at fall's fireworks. Leaf peeping — the act of traveling to witness nature's annual kaleidoscope — contributes billions of dollars to the economy, especially in New England and New York.

But this year, some of the most colorful displays could be in the Midwest. AccuWeather, the commercial forecasting service, said in early September that it expects especially vibrant foliage in states such as Michigan and Illinois.

The service also said powerful, popping colors are expected in upstate New York and parts of Pennsylvania, while New England will follow a more typical color pattern. But that doesn't mean New England travelers will miss out.

Maine, the most forested state in the country, had “an abundance of daily sunshine with just the right amount of rainfall to set the stage for a breathtaking foliage season,” said Gale Ross, the state's fall foliage spokesperson. Color change and timing depend on the weather in the fall, but cooler nighttime temperatures and shorter days should enhance the colors, Ross said.

“The growing season of 2024 has been excellent for trees, supporting tree health and resilience that should lead to brilliant fall colors throughout Maine,” said Aaron Bergdahl, the state's forest pathologist.

Fall colors peak at different times around the U.S., with the foliage season sometimes starting not long after Labor Day in the far northern reaches of the country and extending into November further to the south. In Maine alone, peak foliage can arrive in the northern part of the state in late September and not arrive in coastal areas until close to Halloween.

Leaf turn happens when summer yields to fall and temperatures drop and the amount of sunlight decreases. Chlorophyll in leaves then breaks down, and that allows their fall colors to shine through before leaf drop.

However, weather conditions associated with climate change have disrupted some recent leaf peeping seasons. A warming planet has brought drought that causes leaves to turn brown and wither before reaching peak colors.

Other enemies of leaf peeping include heat waves that cause leaves to fall before autumn arrives and extreme weather events like hurricanes that strip trees of their leaves. A summer heatwave in the Pacific Northwest in 2021 caused a condition called “foliage scorch” that prematurely browned leaves.

This year in Maine, leaf turn was still very sparse in most of the state as late September approached, but the state office of tourism was already gearing up for an influx of tourists. Northern Maine was already experiencing moderate color change. And neighboring New Hampshire was expecting about 3.7 million visitors — more than twice the state's population.

“It’s no surprise people travel from all over the world to catch the incredible color,” said NH Travel and Tourism Director Lori Harnois.