By Chris Spears

DENVER (CBS4) – It’s that time of year! CBS4 viewers are starting to share pictures that show hints of fall color in the mountains of Colorado. So far it’s just little pops of yellow here and there, but it is a sign of what’s to come.

A pop of fall color in Silverthorne, around 9,400 feet. (credit: Mark Mannheimer)

Fall color typically peaks in the higher elevations of the northern mountains during the middle of September and it can last through the end of the month if the weather cooperates. The peak gradually moves south while lowering in elevation as we near the end of September and the first of October.

While you can see color for several weeks, the period between September 25 and October 5, is historically the best. Sometimes you can even catch scenes that include a little dusting of snow on the higher peaks. It makes for a great contrast with the vivid fall color on the trees.

Fall colors ramp up as the production of chlorophyll in deciduous plants and trees slows down and stops. Chlorophyll is what gives leaves their green color during the summer, allowing plants to makes sugars through sunlight, which they will use for food while dormant during the winter.

As the production of chlorophyll tapers off, carotenoids, which produce yellow, orange and brown colors, and anthocyanins, which produce red, purple and blue colors, take over inside the leaf. This process produces a brilliant canvas of color, especially on mountain sides, where large stands of aspen trees intermingle with other species.

Bierstadt Trail in Rocky Mountain National Park (credit: Marsha Hobart)

The weather plays a key role in how vivid the color show will be each year. Some of the best fall color comes when late summer days are dry and sunny and the nights are cool and dry. An occasional light rain helps the process.

These weather conditions allow for a slow and steady conversion of color as the chlorophyll production gradually slows down. Sudden and unseasonable cold snaps and storms with a lot of wind and precipitation can cause the color to not last as long or be very vivid.

Chris Spears