2021 Fall Foliage Peak Map: When Leaves Are Best In Boulder

BOULDER, CO — While many Coloradans venture into the mountains to catch the fall colors, there is still plenty of beauty to be seen in Boulder.

The autumnal equinox is still about a month away on the calendar, but it’s not too early to take a look at the 2021 Fall Foliage Prediction Map to find out when leaves will be the most colorful in Boulder.

The city's foliage is set to peak Sept. 28, according to the map.

No predictive tool is 100 percent accurate, but using the interactive map released Tuesday can give you a pretty good shot at seeing autumn leaves when they turn their most blazing reds, vibrant orange and sunny yellows.

Planning to head outside Boulder? Here are some of the top places to see fall leaves in Colorado:

Golden Gate Canyon State Park

Colorado's beautiful golden aspens are surrounded by evergreens and striking mountain ranges.

San Juan National Forest

The Hermosa Creek Trail allows hikers to view a range of fall colors, and the Piedra Falls Trail includes a waterfall surrounded by foliage.

White River National Forest

Thousands of miles of trails offer hikers a chance to view many landscapes full of colorful fall foliage.

Don't miss the latest news updates in Boulder: Free Boulder Patch Newsletters and Email Alerts | Facebook | Twitter

David Angotti, an expert on statistics who lives in Tennessee, was in the property management business a decade ago when he created the first Fall Foliage Prediction Map to help visitors plan their Great Smoky Mountains vacations when autumn leaves are the most brilliant.

But then they wanted to know about peak leaf peering times in other parts of Tennessee, so he decided to collect data for the entire country.

To use the map, simply slide the scale to the right to see when leaves will peak in your state. Zero in on your county, and you'll be able to decide whether it's best to plan a northern, southern, eastern or western route.

SmokyMountains.com

The tool has developed as a fall vacation planning essential. Last year alone, it received more than 5 million views on SmokyMountains.com and about 30 million more on the news websites, including Patch.

Most people use the leaf map to simply check when foliage will peak near their homes, or to plan a leaf peeping trip.

“However, through the years, we have heard some fascinating stories about how the tool was leveraged,” Angotti said in a news release. “Some of our favorites include a bride in the Northeast changing the date of her outdoor wedding, a director scheduling a movie shoot on location based on our predictions and even a grade school teacher planning a trip to a nearby forest.”

In general, leaves are likely to peak later than usual this year because of prolonged drought conditions across a large swath of the United States, Angotti told Patch. In affected states, leaves may turn from green to brown and skip the brilliant color wheel before “giving up” and falling to the ground, Angotti told Patch.

There’s more than shorter days, longer nights and falling temperatures to signal to trees that it’s time to prepare for winter. The predictive map uses a complex algorithm that analyzes several million data points and spits out about 50,000 predictive data pieces.

This allows for a county-by-county forecast on the precise day the peak should occur. This year, the formula will get a midseason update in late September that will pull in the latest data to increase the accuracy and usefulness of the tool.

The major factors that determine the fall foliage peak are sunlight, precipitation, soil moisture and temperature. They come from a variety of sources including historical precipitation, National Oceanic and Atmospheric Administration precipitation forecasts, elevation, actual temperatures, temperature forecasts and average daylight exposure to develop each county’s fall baseline date.

What Causes The Different Colors

You probably remember from science class that the color change all starts with photosynthesis. Leaves constantly churn out chlorophyll — a key component in a plant’s ability to turn sunlight into the glucose it needs to thrive — from spring through early fall. Those cells saturate the leaves, making them appear green to the human eye.

But leaves aren’t green at all. Autumn is the time for leaves’ big reveal: their true color, unveiled as chlorophyll production grinds to a halt. The colors in fall’s breathtaking tapestry are influenced by other compounds, according to the national park’s website.

Beta carotene, the same pigment that makes carrots orange, reflects the yellow and red light from the sun and gives leaves an orange hue.

The production of anthocyanin, which gives leaves their vivid red color, ramps up in the fall, protecting and prolonging the leaf’s life on a tree throughout autumn.

And those yellows that make you feel as if you’re walking in a ray of sunshine?

They’re produced by flavonol, which is part of the flavonoid protein family. It’s always present in leaves but doesn’t show itself until chlorophyll production begins to slow.