While the month of September has felt a lot more like summer than autumn, more seasonal conditions are on the way next month. In the first Iowa Fall Colors Report this week, several trees are starting to show a bit of color in south central Iowa. The Iowa DNR anticipates peak viewing in the region in the middle of October. According to the report, green ash, cottonwood, silver maple, and walnut are starting to turn yellow, white ash and several shrubs are shifting to purple, ivy and sumac are turning red, but the overall landscape is still mostly green. Dr. Paul Weihe, a professor of biology at Central College, says there are two primary factors that drive the color change on trees every fall.

“One of those would be sort of the yellows, oranges, and golds, and those really are pigments that were present in the plant all along, but those were masked by the green, and that’s what most of us were taught about how color change works,” he says. “But there’s the whole category of colors which are the reds, purples, and some of those really vibrant ones–those are actually produced in response to the changing conditions as we enter the autumn, so those are really acting as a sunscreen to protect the tissues within the leaf, while the tree is recovering some of those materials that the leaf is made out of for recycling and use the following year.”

In the upcoming forecast, according to the National Weather Service and their climate prediction center, chances for rain will increase significantly over the next several weeks, as higher than average precipitation is expected to fall through early October. However, daytime highs this weekend into early next week will remain well above average. The first frost of autumn will also be likely later than normal, with overnight temperatures unlikely to dip below 40 through the end of next week. The typical first frost in south central Iowa is between September 29th and October 3rd, based on long-term climate data. Stay tuned to 92.1 KRLS for the latest weather information.