Monsoonal moisture likely to cause brighter autumn leaves in Summit County |

Monsoonal moisture likely to cause brighter autumn leaves in Summit County

An aspen grove is seen from below on the Sawmill Trail in Breckenridge.
Stephen Giango/Courtesy photo

Hikers and nature enthusiasts alike are anxiously waiting for peak week to spot colorful leaves in Summit County, and the summer’s monsoonal moisture is likely to bring brighter colors to the region this year.

“We typically think about how weather — moving from summer to fall — changes leaves, but realistically, the main driver is the length of night,” Adam Bianchi, Dillon District ranger, said. “So as the days get shorter, and the nights get longer, there’s a biochemical process that starts to occur within the leaves. And that process really starts to affect those pigments. Particularly, it affects chlorophyll.”

Chlorophyll is what gives the leaves their basic green color, and it is produced through photosynthesis that occurs through sunlight. Shorter days, Bianchi said, means less chlorophyll, and colors like red, yellow and orange become more prominent. Warmer days and cooler nights prompt bright colors, which should hit their peak later this month. 

Monsoonal moisture — which has impacted weather conditions and fire restrictions for most of the summer — also has an effect on leaf color. Bianchi said that when there’s ample moisture, trees do not have to delegate resources to the most important places, such as their root systems, rather than in the leaves. 

“That’s a natural piece of the tree trying to deviate its resources, trying to really determine where to best put its resources,” Bianchi said. “If you’ve got a really good spring and summer where it’s wet and the trees had ample amounts of water, and it’s not trying to conserve and it’s been able to make the sugars out of that sunlight that, when it does change, it’s going to be very bright colors. It’s not going to be the dull brown colors. ”

Currently, September is tied to break the record for the warmest September in the past 22 years at 81 degrees.

In 2021, color-changing on trees across the state was delayed about 10 days because of above-normal temperatures. Experts at the time said there were less vibrant colors in those areas, with shorter durations of color.

Predictions from, which tracks peak foliage colors across the United States, has its current predictions for Summit County falling between Sept. 26 and Oct. 10. 

Predictions from show that the last week in September and the first few days of October will likely be peak week for leaf-peeping in Summit County.

The Climate Prediction Center’s latest two-week outlook has Summit County temperatures to be likely above normal, much like the rest of the Mountain West and across the Great Plains. Precipitation is expected to be below normal. 

David Barjenbruch, a meteorologist at the National Weather Service in Boulder, said that a series of cold fronts is expected to hit the region within the next few days, bringing some relief to warmer weather. Remnants of Hurricane Kay in the Pacific Ocean will bring a higher chance of showers and storms toward Tuesday and Wednesday, especially in the High Country, he added.

“It still looks cold enough for a little snow in the mountains above 9,000-10,000 feet, although precipitation amounts are looking fairly light yet,” Barjenbruch said. “Drier weather should develop by Sunday, with warmer temperatures, but readings still a few degrees below normal.”

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