Utah's fall colors are starting to show. When will they peak?

SALT LAKE CITY — Meteorologically speaking, fall is already here and one of the more colorful periods in Utah is just around the corner.

Carol Dyer sent KSL photos of patchy fall colors starting to show in the mountains near Bear Lake on Wednesday. Others have submitted photos through KSL.com's Witness over the past few days, showing trees in other parts of the state beginning to change as astronomical summer comes to a close.

It's only a matter of time before Utah's mountains, canyons and valleys will eventually become a mix of red, orange and yellow. The process typically begins when warm days are followed by cool evenings, a pattern that has reached Utah recently.

When will Utah's trees peak this fall?

There isn't a scientific way of knowing when the process of changing colors will play out, but SmokyMountains.com has become the leader in predictions across the state and the rest of the continental U.S. The website — first created to provide information for the scenic Smoky Mountains in the southeast — uses long-range forecasts, past trends and weather data, user-submitted observations and information about regional tree types to project when tree colors might peak in every region.

It projected that the process would pick up at about this point in the season in Utah's northern mountains, which is usually the case. The region is often one of the first parts of the country where fall colors begin to show, largely because of its elevation.

The website projects that the process will continue to ramp up in the coming weeks before it estimates that the Wasatch Mountains reach peak near the end of September or the start of October. By then, other parts of Utah's northern half are expected to be either in the partial or near peak processes.

Some of this can be tricky to piece together within Utah's counties because trees often peak in higher elevations before the valleys. However, the website SmokyMountains.com projects that most of Utah's northern half will have reached peak or close to it by mid-October while the process picks up steam in southern Utah.

Its forecast estimates that southern Utah will peak by the end of October or the start of November, while the rest of the state reaches past peak. Northern Utah valleys may still be colorful around this time because of the elevation difference with the mountains.

Utah's peak isn't expected to be one of the first in the country this year, though.

SmokyMountains.com anticipates leaves will peak across the country's northern border first, from northern Washington and Idaho all the way to New England. Some of those could peak in late September and begin to fade by early October.

Those wishing to chase fall colors as long as possible may want to plan trips to the southeast. Peak colors may not reach parts of that region until early- to mid-November.

The science behind the colors

So what's behind the magic?

The changing of the leaves has everything to do with photosynthesis, as you may remember from elementary education.

Chlorophyll, a major element in the photosynthesis process, produces a green pigment in leaves, the U.S. Forest Service points out. However, as a tree's energy process dies down toward the end of summer, it stops producing chlorophyll and a tree's true colors appear.

A leaf's true colors are based on pigments that are masked by chlorophyll during the spring and summer. Leaves with carotenoids can turn orange or yellow, while yellow leaves typically also have flavonoids. Red leaves are tied to anthocyanins.

For those curious about what tree they are looking at this fall, Utah State University's Forest Extension compiled a list of tree species commonly found in the state's wild spaces.

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