This past weekend marked the official arrival of fall in Colorado, as cooler temperatures and a stormy system swept through the region. While the mountains saw their first significant snowfall of the season, many across the plains experienced a marked drop in temperatures, signaling the end of summer. The system brought rain and snow to higher elevations above 9,000 feet, with modest rainfall in lower areas, offering some relief to drought-stricken regions.
As the storm cleared out Sunday afternoon, temperatures remained well below normal for this time of year, adding to the seasonal shift. While the storm hinted at the arrival of autumn, a different trend may become the reality for the weeks ahead. The outlook for the next month calls for below-average precipitation and warmer-than-normal temperatures, suggesting that the lingering warmth of summer will stretch into much of October. Despite this, the change in seasons is underway, and the anticipation of more frequent snowfalls in the mountains will grow as we move deeper into fall.
Beyond the weather changes, this season also brings the vibrant colors that define autumn. Many assume that cold weather is solely responsible for the transformation in leaves, but the process is much more complex. According to the National Weather Service, the change in leaf color is the result of chemical processes occurring within the trees as the seasons transition.
Throughout spring and summer, leaves produce food through photosynthesis, thanks to chlorophyll, the green pigment in the leaves that absorbs sunlight. As fall approaches and daylight shortens, cooler temperatures cause this process to slow. The chlorophyll begins to break down, revealing the yellow and orange pigments that were hidden beneath the green. The brilliant reds and purples some trees exhibit come from sugars trapped in the leaves, which react with cooler, but not freezing, nighttime temperatures.
The most striking fall colors emerge when the days are warm and sunny, and the nights are cool but not freezing (in other words, right around now!). Hard frosts can cut this process short, causing leaves to wither and fall before they fully change. Rainy and cloudy weather can also dull the vibrancy of autumn colors, making sunny fall days a key ingredient for spectacular displays.
While the current forecast predicts warmer-than-usual conditions and drier weather for much of Colorado, the gradual shift into fall is inevitable. Whether it’s the changing foliage or the first snow-dusted peaks, nature’s signals remind us that autumn is officially here, and soon, cooler days and brilliant landscapes will follow.